Semiconductor device and a method for manufacturing a semiconductor device

ABSTRACT

The characteristics of a semiconductor device are improved. A semiconductor device has a potential fixed layer containing a p type impurity, a channel layer, and a barrier layer, formed over a substrate, and a gate electrode arranged in a trench penetrating through the barrier layer, and reaching some point of the channel layer via a gate insulation film. Source and drain electrodes are formed on opposite sides of the gate electrode. The p type impurity-containing potential fixed layer has an inactivated region containing an inactivating element such as hydrogen between the gate and drain electrodes. Thus, while raising the p type impurity (acceptor) concentration of the potential fixed layer on the source electrode side, the p type impurity of the potential fixed layer is inactivated on the drain electrode side. This can improve the drain-side breakdown voltage while providing a removing effect of electric charges by the p type impurity.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2014-176367 filed onAug. 29, 2014 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to a semiconductor device, and ispreferably applicable to, for example, a semiconductor device using anitride semiconductor.

In recent years, attention has been paid to semiconductor devices eachusing a III-V group compound having a larger bandgap than that ofsilicon (Si). Among them, a MISFET using gallium nitride (GaN) hasadvantages such as 1) large breakdown electric field, 2) large saturatedelectron velocity, 3) large thermal conductivity, 4) being able to forma favorable hetero junction between AlGaN and GaN, and 5) being anontoxic and high-safety material.

For example, in Patent Document 1 (Japanese Unexamined PatentApplication Publication No. 2010-109086), there is disclosed a nitridesemiconductor device in which a p-GaN layer is arranged under a channellayer formed of an undoped GaN layer. Then, the p-GaN layer iselectrically coupled with a source electrode, thereby to achieve a highavalanche resistance and high reliability.

Patent Document [Patent Document 1] Japanese Unexamined PatentApplication Publication No. 2010-109086 SUMMARY

The present inventors have been involved in research and development ofthe semiconductor devices using a nitride semiconductor as describedabove, and have conducted a close study on the improvement of thecharacteristics. During the process thereof, it has been proved thatthere is room for further improvement of the characteristics of thesemiconductor device using a nitride semiconductor.

Other objects and novel features will be apparent from the descriptionof this specification and the accompanying drawings.

Summaries of the representative ones of the embodiments disclosed in thepresent application will be described in brief as follows.

A semiconductor device shown in one embodiment disclosed in the presentapplication has a potential fixed layer containing an impurity, and agate electrode. Then, on the opposite sides of the gate electrode, thereare formed a source electrode and a drain electrode, respectively. Thepotential fixed layer including an impurity has an inactivated regioncontaining an inactivating element such as hydrogen between the gateelectrode and the drain electrode.

A method for manufacturing a semiconductor device shown in oneembodiment disclosed in the present application has a step of forming apotential fixed layer containing an impurity, and a gate electrode.Then, the method has a step of introducing an inactivating element intothe potential fixed layer situated on one side of the gate electrode.Further, the method has a step of forming a source electrode over thepotential fixed layer on the other side of the gate electrode, andforming a drain electrode over the potential fixed layer on the oneside.

In accordance with the semiconductor devices shown in the followingrepresentative embodiments disclosed in the present application, it ispossible to improve the characteristics of the semiconductor devices.

In accordance with the methods for manufacturing a semiconductor deviceshown in the following representative embodiments disclosed in thepresent application, it is possible to manufacture a semiconductordevice having favorable characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view schematically showing a configurationof a semiconductor device of First Embodiment;

FIG. 2 is a plan view showing a configuration of the semiconductordevice of First Embodiment;

FIG. 3 is a cross sectional view showing a configuration of thesemiconductor device of First Embodiment;

FIG. 4 is a cross sectional view showing a configuration of thesemiconductor device of First Embodiment;

FIG. 5 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step;

FIG. 6 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 5;

FIG. 7 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step;

FIG. 8 is a plan view showing the semiconductor device of FirstEmbodiment during a manufacturing step;

FIG. 9 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 6;

FIG. 10 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 7;

FIG. 11 is a plan view showing the semiconductor device of FirstEmbodiment during a manufacturing step;

FIG. 12 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 9;

FIG. 13 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 10;

FIG. 14 is a plan view showing the semiconductor device of FirstEmbodiment during a manufacturing step;

FIG. 15 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 12;

FIG. 16 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 13;

FIG. 17 is a plan view showing the semiconductor device of FirstEmbodiment during a manufacturing step;

FIG. 18 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 15;

FIG. 19 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 16;

FIG. 20 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 18;

FIG. 21 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 19;

FIG. 22 is a plan view showing the semiconductor device of FirstEmbodiment during a manufacturing step;

FIG. 23 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 20;

FIG. 24 is a cross sectional view showing the semiconductor device ofFirst Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 21;

FIG. 25 is a plan view showing the semiconductor device of FirstEmbodiment during a manufacturing step;

FIG. 26 is a graph showing the relationship between the longitudinaldrain breakdown voltage and the activated acceptor concentration in apotential fixed layer;

FIG. 27 is a cross sectional view showing a configuration of asemiconductor device of Applied Example 1 of First Embodiment;

FIG. 28 is a cross sectional view showing a configuration of asemiconductor device of Applied Example 2 of First Embodiment;

FIG. 29 is a cross sectional view schematically showing a configurationof a semiconductor device of Applied Example 3 of First Embodiment;

FIG. 30 is a cross sectional view schematically showing a configurationof a semiconductor device of Second Embodiment;

FIG. 31 is a cross sectional view showing a configuration of thesemiconductor device of Second Embodiment;

FIG. 32 is a cross sectional view showing a configuration of thesemiconductor device of Second Embodiment;

FIG. 33 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step;

FIG. 34 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step;

FIG. 35 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 33;

FIG. 36 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 34;

FIG. 37 is a plan view showing the semiconductor device of SecondEmbodiment during a manufacturing step;

FIG. 38 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 35;

FIG. 39 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 36;

FIG. 40 is a plan view showing the semiconductor device of SecondEmbodiment during a manufacturing step;

FIG. 41 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 38;

FIG. 42 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 39;

FIG. 43 is a plan view showing the semiconductor device of SecondEmbodiment during a manufacturing step;

FIG. 44 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 41;

FIG. 45 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 42;

FIG. 46 is a plan view showing the semiconductor device of SecondEmbodiment during a manufacturing step;

FIG. 47 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 44;

FIG. 48 is a cross sectional view showing the semiconductor device ofSecond Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 45;

FIG. 49 is a plan view showing the semiconductor device of SecondEmbodiment during a manufacturing step;

FIG. 50 is a cross sectional view schematically showing a configurationof a semiconductor device of Third Embodiment;

FIG. 51 is a cross sectional view showing the semiconductor device ofThird Embodiment during a manufacturing step;

FIG. 52 is a cross sectional view showing the semiconductor device ofThird Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 51;

FIG. 53 is a cross sectional view showing the semiconductor device ofThird Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 52;

FIG. 54 is a cross sectional view showing the semiconductor device ofThird Embodiment during a manufacturing step;

FIG. 55 is a cross sectional view showing the semiconductor device ofThird Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 53;

FIG. 56 is a cross sectional view showing the semiconductor device ofThird Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 54;

FIG. 57 is a cross sectional view schematically showing a configurationof a semiconductor device of Fourth Embodiment;

FIG. 58 is a cross sectional view showing the semiconductor device ofFourth Embodiment during a manufacturing step;

FIG. 59 is a cross sectional view showing the semiconductor device ofFourth Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 58;

FIG. 60 is a cross sectional view showing the semiconductor device ofFourth Embodiment during a manufacturing step, and showing themanufacturing step following FIG. 59;

FIG. 61 is a cross sectional view schematically showing a configurationof a semiconductor device of Fifth Embodiment;

FIG. 62 is a cross sectional view showing a configuration of thesemiconductor device of Fifth Embodiment;

FIG. 63 is a plan view showing a configuration of the semiconductordevice of Fifth Embodiment;

FIGS. 64A and 64B are cross sectional views schematically showing otherconfigurations of the semiconductor device of Fifth Embodiment; and

FIG. 65 is across sectional view schematically showing anotherconfiguration of the semiconductor device of Fifth Embodiment.

DETAILED DESCRIPTION

In description of the following embodiment, the embodiment may bedescribed in a plurality of divided sections or embodiments forconvenience, if required. However, unless otherwise specified, these arenot independent of each other, but are in a relation such that one is amodification example, an applied example, a detailed description,complementary explanation, or the like of a part or the whole of theother. Further, in the following embodiments, when a reference is madeto the number of elements, and the like (including number, numericalvalue, quantity, range, or the like), the number of elements is notlimited to the specific number, but may be greater than or less than thespecific number, unless otherwise specified, except for the case wherethe number is apparently limited to the specific number in principle, orexcept for other cases.

Further, in the following embodiments, the constitutional elements(including element steps, or the like) are not always essential, unlessotherwise specified, except for the case where they are apparentlyconsidered essential in principle, or except for other cases. Similarly,in the following embodiments, when a reference is made to the shapes,positional relationships, or the like of the constitutional elements, orthe like, it is assumed that they include ones substantially analogousor similar to the shapes or the like, unless otherwise specified, unlessotherwise considered apparently in principle, or except for other cases.This also applies to the foregoing numbers and the like (includingnumbers, numerical values, ranges, and the like).

Below, embodiments will be described in details by reference to theaccompanying drawings. Incidentally, in all the drawings for describingthe following embodiments, the members having the same function aregiven the same or related reference signs and numerals, and a repeateddescription thereon is omitted. Further, when a plurality of similarmembers (portions) are present, a sign may be added to a genericreference numeral to denote an individual or specific portion. Further,in the following embodiments, unless particularly necessary, the same orsimilar portions will not be repeatedly described.

Further, in the accompanying drawings used in embodiments, hatching maybe omitted even in a cross sectional view for ease of understanding ofthe drawings. Whereas, hatching may be added even in a plan view forease of understanding of the drawings.

Further, in a cross sectional view and a plan view, the dimensions ofeach part are not intended to correspond to those of an actual device.For ease of understanding of the drawing, a specific part may be shownon a relatively larger scale. Further, also when a cross sectional viewand a plan view correspond to each other, for ease of understanding ofthe drawings, a specific part may be shown on a relatively larger scale.

First Embodiment

Below, with reference to the accompanying drawings, a semiconductordevice of the present embodiment will be described in details.

[Structure Description]

FIG. 1 is a cross sectional view schematically showing a configurationof a semiconductor device of the present embodiment. The semiconductordevice (semiconductor element) of the present embodiment shown in FIG.1, or the like is a MIS (Metal Insulator Semiconductor) type FET (FieldEffect Transistor) using a nitride semiconductor. The semiconductordevice can be used as a HEMI (High Electron Mobility Transistor) typepower transistor. The semiconductor device of the present embodiment isa so-called recess gate type semiconductor device.

In the semiconductor device of the present embodiment, over a substrateS, there are sequentially formed a nucleation layer NUC, a buffer layerBU, a potential fixed layer VS, a channel base layer UC, a channel layer(also referred to as an electron transit layer) CH, and a barrier layerBA. The nucleation layer NUC is formed of a nitride semiconductor layer.The buffer layer BU is formed of a single layered or multilayerednitride semiconductor layer doped with an impurity for forming a deeplevel in a nitride semiconductor. Herein, there is used a superlatticestructure (also referred to as a superlattice layer) formed of amultilayered nitride semiconductor layer. The potential fixed layer VCis formed of a nitride semiconductor layer doped with an impurity toproduce a p type with respect to a nitride semiconductor, and has aconductivity. The channel base layer UC is formed of a nitridesemiconductor layer smaller in electron affinity than the channel layerCH, and smaller in average lattice constant in the substrate surfacedirection than the channel layer CH. The channel layer CH is formed of anitride semiconductor layer larger in electron affinity than the channelbase layer UC. The barrier layer BA is formed of a nitride semiconductorlayer smaller in electron affinity than the channel layer CH, andsmaller in electron affinity than the channel base layer UC. Over thebarrier layer BA, there is formed an insulation film (not shown).Incidentally, a cap layer may be provided between the insulation film(protective film) and the barrier layer BA. The cap layer s formed of anitride semiconductor layer larger in electron affinity than the barrierlayer BA.

The MISFET of the present embodiment has a gate electrode GE formed overthe channel layer CH via a gate insulation film GI, and a sourceelectrode SE and a drain electrode DE formed over the barrier layer BAon the opposite sides of the gate electrode GE, respectively. The MISFETis formed in an active region AC defined by isolation regions ISO.Further, the gate electrode GE is formed in the inside of a trench Tpenetrating through the barrier layer BA, and reaching some point of thechannel layer CH via the gate insulation film GI.

On the channel layer CH side in the vicinity of the interface betweenthe channel layer CH and the barrier layer BA, there is formed atwo-dimensional electron gas (2DEG). Whereas, when the gate electrode GEis applied with a positive potential (threshold potential), a channel isformed in the vicinity of the interface between the gate insulation filmGI and the channel layer CH.

The two-dimensional electron gas (2DEG) is formed by the followingmechanism. The nitride semiconductor layers (herein, gallium nitridetype semiconductor layers) forming the channel layer CH and the barrierlayer BA respectively have different electron affinities (forbidden bandwidths (bandgaps)). The barrier layer BA is formed of a nitridesemiconductor layer smaller in electron affinity than the channel layerCH. For this reason, at the junction surface of the semiconductorlayers, there is formed a well type potential. The accumulation ofelectrons in the well type potential results in the formation of thetwo-dimensional electron gas (2DEG) in the vicinity of the interfacebetween the channel layer CH and the barrier layer BA. Particularly,herein, the channel layer CH and the barrier layer BA are epitaxiallyformed with a gallium (or aluminum) plane grown nitride semiconductormaterial. For this reason, positive fixed polarization charges aregenerated at the interface between the channel layer CH and the barrierlayer BA. Thus, electrons are accumulated in order to neutralize thepositive polarization charges. Accordingly, the two-dimensional electrongas (2DEG) becomes more likely to be formed.

Then, the two-dimensional electron gas (2DEG) formed in the vicinity ofthe interface between the channel layer CH and the barrier layer BA isdivided by the trench T including the gate electrode GE formed therein.For this reason, in the semiconductor device of the present embodiment,with the gate electrode GE not applied with a positive potential(threshold potential), the OFF state can be kept; and with the gateelectrode GE applied with a positive potential (threshold potential),the ON state can be kept. Thus, the normally off operation can beperformed. Incidentally, in the ON state and the OFF state, thepotential of the source electrode SE is, for example, the groundpotential.

Further, the channel layer CH is interposed between the barrier layer BAand the channel base layer UC smaller in electron affinity than thechannel layer CH, resulting in an improvement of the electron confiningeffect. This enables the suppression of the short channel effect, theamplification factor improvement, and the improvement of the operationspeed. Further, when the channel base layer UC undergoes a tensilestrain, to be strained, negative charges due to the piezo polarizationand the spontaneous polarization are induced at the interface betweenthe channel base layer UC and the channel layer CH. Accordingly, thethreshold potential moves to the positive side. This can improve thenormally off operation property. Whereas, when the strain of the channelbase layer UC is relaxed, negative charges due to the spontaneouspolarization are induced at the interface between the channel base layerUC and the channel layer CH. Accordingly, the threshold potential movesto the positive side. This can improve the normally off operationproperty.

Herein, in the present embodiment, in the isolation region ISO, there isprovided a coupling part (also referred to as a via) VIA penetratingthrough the isolation region ISO, and reaching the underlying potentialfixed layer VC. The coupling part VIA is electrically coupled with thesource electrode SE. Thus, the potential fixed layer VC is provided, andcoupled with the source electrode SE. As a result, it is possible toreduce the fluctuations in characteristics such as the thresholdpotential and the ON resistance.

Further, in the present embodiment, the coupling part VIA in the throughhole TH is arranged in the isolation region ISO outside the activeregion AC in which electrons are conducted, and under the formationregion of the source pad SP. As a result, it is possible to implementminiaturization and high integration of semiconductor devices. Further,it is possible to ensure a large active region AC in which electrons canbe conducted. For this reason, it is possible to reduce the ONresistance per unit area.

Further, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Theinactivated region IR reaches the potential fixed layer VC in the depthdirection. Thus, the potential fixed layer VC doped with an impurity toproduce a p type situated between the gate electrode GE and the drainelectrode DE is inactivated by doping with an inactivating element, tobe the inactivated region IR. As a result, it is possible to improve thedrain breakdown voltage.

The p type potential fixed layer VC situated between the gate electrodeGE and the drain electrode DE contains an inactivating element. Then,the content of the inactivating element of the p type potential fixedlayer VC situated between the gate electrode GE and the drain electrodeDE is larger than the content of the inactivating element of the p typepotential fixed layer VC situated under the source electrode SE. Theinactivating element is, for example, hydrogen (H) or fluorine (F).

Herein, inactivation indicates the ratio of the density of the acceptorto the density of the impurity to produce a p type. The activation ratioof the inactivated region IR is smaller than, and is preferably set at1/10 or less the activation ratio of the region under the sourceelectrode SE. In other words, in the potential fixed layer VC, theactivation ratio of the potential fixed layer situated under the drainelectrode (also referred to as a drain-side potential fixed layer) VC issmaller than, and is preferably 1/10 or less the activation ratio of thepotential fixed layer situated under the source electrode (also referredto as a source-side potential fixed layer) VC. As described later, whenas the potential fixed layer VC, there is used a gallium nitride layerepitaxially grown while being doped with magnesium (Mg) which is a ptype impurity, the p type impurity is roughly uniformly introduced intothe potential fixed layer VC. Then, an inactivating element such ashydrogen (H) is ion-implanted into the drain-side potential fixed layerVC. As a result, the drain-side potential fixed layer VC is inactivated.In such a case, also in the drain-side potential fixed layer VC, a Mgelement which is a p type impurity is introduced at a density comparableto that of the source side, but ceases to contribute as an acceptorunder the influence of H which is an inactivating element. Thus, in thedrain-side potential fixed layer VC, the ratio of the density of theacceptor to the density of the impurity to produce a p type is lowerthan that of the source side. The activation ratio can be estimated bymeasuring, for example, the voltage dependency of the capacitance (CV).

With reference to FIGS. 2 to 4, the semiconductor device of the presentembodiment will be further described in details. FIG. 2 is a plan viewshowing a configuration of the semiconductor device of the presentembodiment. FIGS. 3 and 4 are each a cross sectional view showing aconfiguration of the semiconductor device of the present embodiment.FIG. 3 corresponds to a cross section along A-A of FIG. 2. FIG. 4corresponds to a cross section along B-B of FIG. 2.

As shown in FIG. 2, the planar shape of the drain electrode DE is arectangular shape having long sides in the Y direction. A plurality ofdrain electrodes DE each in a line shape are arranged at a giveninterval in the X direction. Whereas, the planar shape of the sourceelectrode SE is a rectangular shape having long sides in the Ydirection. A plurality of source electrodes SE each in a line shape arearranged at a given interval in the X direction. Then, the plurality ofsource electrodes SE and the plurality of drain electrodes DE arealternately arranged along the X direction, respectively.

Under the drain electrode DE, there is arranged a contact hole C1Dserving as the coupling part between the drain electrode DE and the caplayer CP (barrier layer BA). The planar shape of the contact hole C1D isa rectangular shape having long sides in the Y direction. Under thesource electrode SE, there is arranged a contact hole C1S serving as thecoupling part between the source electrode SE and the cap layer CP(barrier layer BA). The planar shape of the contact hole C1S is arectangular shape having long sides in the Y direction.

Then, between the contact hole C1D under the drain electrode DE and thecontact hole C1S under the source electrode SE, there is arranged a gateelectrode GE. The gate electrode GE has a rectangular shape having longsides in the Y direction. Under one source electrode SE, there arearranged two (a pair of) gate electrodes GE. The two gate electrodes GEare arranged on the opposite sides of the contact hole C1S under thesource electrode SE, respectively. Thus, two gate electrodes GE arerepeatedly arranged for each of the plurality of source electrodes SE.

The plurality of drain electrodes DE are coupled by a drain pad (alsoreferred to as a terminal part) DP. The drain pad DP is arranged in sucha manner as to extend in the X direction on one end side of the drainelectrode DE (the lower side in FIG. 2). In other words, a plurality ofdrain electrodes DE are arranged in such a manner as to protrude in theY direction from the drain pad DP extending in the X direction. Such ashape may be referred to as a comb shape.

The plurality of source electrodes SE are coupled by a source pad (alsoreferred to as a terminal part) SP. The source pad SP is arranged insuch a manner as to extend in the X direction on the other end side ofthe source electrode SE (the upper side in FIG. 2). In other words, theplurality of source electrodes SE are arranged in such a manner as toproject in the Y direction from the source pad SP extending in the Xdirection. Such a shape may be referred to as a comb shape.

The plurality of gate electrodes GE are coupled by a gate line GL. Thegate line GL is arranged in such a manner as to extend in the Xdirection on one end side of the gate electrode GE (the upper side inFIG. 2). In other words, the plurality of gate electrodes GE arearranged in such a manner as to protrude in the Y direction from thegate line GL extending in the X direction. Incidentally, the gate lineGL is coupled with, for example, the gate pads (not shown) provided onthe opposite sides of the gate line GL in the X direction (the rightside and the left side in FIG. 2).

Herein, the source electrode SE, the drain electrode DE, and the gateelectrode GE are mainly arranged over the active region AC surrounded bythe isolation regions ISO. The planar shape of the active region AC is arectangular shape having long sides in the X direction (see FIG. 8). Onthe other hand, the drain pad DP, the gate line GL, and the source padSP are formed over the isolation region ISO. Between the active regionAC and the source pad SP, there is arranged the gate line GL.

Then, under the source pad SP, there is arranged a through hole (alsoreferred to as a hole, opening, or concave part) TH. A conductive filmis embedded in the through hole TH, and forms a coupling part VIA. Asdescribed later, the coupling part VIA is electrically coupled with thepotential fixed layer VC. Accordingly, the source electrode SE and thepotential fixed layer VC are electrically coupled with each other viathe source pad SP and the coupling part VIA.

Herein, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Theinactivated region IR is a region doped with an element (an inactivatingelement) for inactivating the impurity in the potential fixed layer VC.Incidentally, the inactivated region IR also extends under the drainelectrode DE (see FIG. 17).

As shown in FIGS. 3 and 4, the MISFET of the present embodiment has thegate electrode GE formed over the active region AC of the substrate S,and the source electrode SE and the drain electrode DE formed over thecap layer CP on the opposite sides of the gate electrode GE, and in theformation regions of the contact holes (C1S and C1D), respectively. Overthe source electrode SE and the drain electrode DE, there is arranged aprotective film (also referred to as an insulation film, a coveringfilm, or a surface protective film) PRO.

Over the substrate S, as described previously, there are sequentiallyformed the nucleation layer NUC, the buffer layer BU, the potentialfixed layer VC, the channel base layer UC, the channel layer (alsoreferred to as an electron transit layer) CH, the barrier layer BA, thecap layer CP, and the insulation film IF1. Then, the gate electrode GEis formed in the inside of a trench T penetrating through the insulationfilm IF1, the cap layer CP, and the barrier layer BA, and reaching somepoint of the channel layer CH via the gate insulation film GI.

As the substrate S, there can be used a semiconductor substrate formedof, for example, silicon (Si). As the substrate S, there may be used asubstrate formed of a nitride semiconductor such as GaN other than thesilicon, or there may be used a substrate formed of AlN, SiC, sapphire,or the like. Especially, when a nitride semiconductor layer such as aGaN layer is formed over a silicon substrate, the buffer layer BU isoften used as described later in order to improve the crystallinitythereof, or to relax the strain (internal stress) of the substrate.Accordingly, accumulation of electric charges described later tends tooccur. For this reason, when a silicon substrate and a nitridesemiconductor are used in combination, the semiconductor device of thepresent embodiment is effectively used.

The nucleation layer NUC is formed in order to generate the crystallinenucleus for the growth of a layer to be formed thereover such as thebuffer layer BU. Further, the nucleation layer NUC is formed in order toprevent the deterioration of the substrate S due to diffusion of theconstituent elements (such as Ga) of the layer formed thereover into thesubstrate S from the layer formed thereover. As the nucleation layerNUC, there can be used, for example, an aluminum nitride (AlN) layer.The film thickness of the AlN layer is about 200 nm. The material andthe thickness of the nucleation layer NUC can be appropriately selectedaccording to the material for the substrate S, or the use of thesemiconductor device. Alternatively, the nucleation layer NUC can beomitted when a GaN substrate or the like is used as the substrate S, orwhen not necessary according to the deposition conditions for the bufferlayer or the like.

The buffer layer BU is formed in order to adjust the lattice constant,to make favorable the crystallinity of the nitride semiconductor to beformed thereover, and to relax the film stress of the nitridesemiconductor to be stacked. This improves the crystallinity of thenitride semiconductor. Further, the strain (internal stress) of thesubstrate S can be relaxed, so that the substrate S can be inhibitedfrom undergoing warpage or cracks. As the buffer layer BU, there can beused a superlattice structure in which lamination films (AlN/GaN films)each of a gallium nitride (GaN) layer and an aluminum nitride (AlN)layer are deposited a plurality of cycles. The superlattice structureincludes two or more laminates of nitride semiconductor layers havingdifferent electron affinities repeatedly arranged therein. Thesuperlattice structure is doped with carbon (C). For example, the filmthickness of the GaN layer is set at about 20 nm, and the film thicknessof the AlN layer is set at about 5 nm. There can be used a superlatticestructure including the lamination films deposited 80 cycles. The carbonconcentration (dope amount) is, for example, about 1×10¹⁹ (1E19) cm⁻³.However, the material and the thickness of each film forming thelamination film may be appropriately selected according to the use ofthe semiconductor device. Further, the buffer layer BU may include alayer other than the superlattice structure. For example, anothermaterial film may be formed over the superlattice structure.Alternatively, as the buffer layer BU, there can also be used a singlelayer film not including a superlattice structure, or the like.

As the materials for the superlattice structure and the single layerfilm, InN can be used other than AlN and GaN. Alternatively, a mixedcrystal of the nitride semiconductors may also be used. For example, asthe lamination film of a superlattice structure, an AlGaN/GaN film canbe used other than an AlN/GaN film. Whereas, as the monolayer film,there can be used, for example, an AlGaN layer or an InAlN layer.

Further, in the foregoing description, the superlattice structure isdoped therein with carbon. However, other doping impurities may be used.As the doping impurities, elements forming a deep level are preferable.Other than carbon, there may be used a transition metal such as iron(Fe), magnesium (Mg), beryllium (Be), or the like. The dope amount andthe impurity element may be appropriately selected according to the useof the semiconductor device.

As the potential fixed layer VC, there may be used, for example, a GaNlayer doped with an impurity. Other than the GaN layer, there may alsobe used an AlN layer, an InN layer, or an AlGaN layer. Alternatively, amixed crystal of the nitride semiconductors may be used.

The potential fixed layer VC is doped with an impurity, and has aconductivity. For example, as the potential fixed layer VC, there can beused a GaN layer doped with Mg in an amount of about 5×10¹⁸ (5E18) cm⁻³as an impurity. The film thickness of the potential fixed layer VC isabout 200 nm.

Thus, an impurity is required to be doped in an amount sufficient tocause the conductivity (e.g., with the layer structure of the presentembodiment, the dope amount is 5×10¹⁶ (5E16) cm⁻³ or more in terms ofthe activated impurity concentration). As the doping impurity, there canbe used a p type impurity. As the p type impurity, for example, mentionmay be made of Be, C, or Mg. Whereas, from the viewpoint of thelongitudinal breakdown voltage, the dope amount of the impurity ispreferably 1×10¹⁸ (1E18) cm⁻³ or less in terms of the activated impurityconcentration. For example, in the layer structure of the presentembodiment, in order to ensure 500 V or more as the longitudinalbreakdown voltage, the dope amount is preferably set at 5×10¹⁷ (5E17)cm⁻³ or less in terms of the activated impurity concentration.

As the channel base layer UC, there can be used, for example, an AlGaNlayer. The channel base layer UC is not subjected to intentionalimpurity doping therein. Incidentally, the formation of a deep level byimpurity doping causes fluctuations in characteristics such as thethreshold potential as described in details later. Accordingly, the dopeamount of the impurity is preferably 1×10¹⁶ (1E16) cm⁻³ or less.

Whereas, the thickness of the AlGaN layer is, for example, 1000 nm, andthe composition of Al is about 3%. As the channel base layer UC, otherthan an AlGaN layer, there can be used an InAlN layer, or the like.

Further, in the present embodiment, the lattice constant in the in-planedirection of the channel base layer UC is taken over to the channellayer CH and the barrier layer BA thereover by epitaxial growth. Forexample, when at a layer over the channel base layer UC, there is formeda layer having a larger lattice constant than that of the channel baselayer (AlGaN layer) UC such as a GaN layer, an In_(X)Ga_((1-X))N layer(0≦X≦1), or an InAlN layer, the overlying layer is applied with acompressive strain. Conversely, when at a layer over the channel baselayer UC, there is formed a layer having a smaller lattice constant thanthat of the channel base layer (AlGaN layer) UC such as an InAlN layerwith a high Al composition ratio, the overlying layer is applied with atensile strain.

As the channel layer CH, there can be used, for example, a GaN layer.The channel layer CH is not subjected to intentional impurity dopingtherein. Whereas, the thickness of the GaN layer is, for example, about80 nm. As the materials for the channel layer CH, other than GaN, therecan be used AlN, InN, and the like. Alternatively, a mixed crystal ofthe nitride semiconductors may be used. The material and the thicknessof the channel layer CH can be appropriately selected according to theuse of the semiconductor device. Incidentally, in the presentembodiment, the nondoped channel layer CH was used. However, an impuritymay be appropriately doped according to the use. As the doping impurity,there can be used an n type impurity or a p type impurity. Examples ofthe n type impurity may include Si, S, and Se. Examples of the p typeimpurity may include Be, C, and Mg.

However, the channel layer CH is a layer in which electrons run. Forthis reason, when the dope amount of the impurity is too large, themobility may be reduced by the Coulomb scattering. Thus, the dope amountof the impurity into the channel layer CH is preferably 1×10¹⁷ (1E17)cm⁻³ or less.

Further, for the channel layer CH, it is necessary to use a nitridesemiconductor larger in electron affinity than the channel base layer UCor the barrier layer BA. As described above, as the channel base layerUC, there is used an AlGaN layer, and as the channel layer CH, there isused a GaN layer. Thus, when the lattice constants of the layers aredifferent, the film thickness of the channel layer CH is required to beequal to, or smaller than the critical film thickness from whichdislocation increases.

As the barrier layer BA, there can be used, for example, anAl_(0.2)Ga_(0.8)N layer. Whereas, the thickness of the Al_(0.2)Ga_(0.8)Nlayer is, for example, about 30 nm. As the materials for the barrierlayer BA, other than the AlGaN layer, there may be used an InAlN layer,and the like. The composition ratio of Al, or the like may beappropriately adjusted. Alternatively, there may also be used a barrierlayer BA of a multilayer structure resulting from lamination of filmshaving different Al composition ratios. Further, as the materials forthe barrier layer BA, there can be used a GaN layer, an AlN layer, anInN layer, and the like. Alternatively, a mixed crystal of the nitridesemiconductors may be used. The material and the thickness of thebarrier layer BA, and the like can be appropriately selected accordingto the use of the semiconductor device. Incidentally, as the barrierlayer BA, there may be used a nondoped layer, and an impurity may beappropriately doped according to the use. As the doping impurity, therecan be used an n type impurity or a p type impurity. Examples of the ntype impurity may include Si, S, and Se. Examples of the p type impuritymay include Be, C, and Mg. However, when the dope amount of the impurityin the barrier layer BA is too large, in the vicinity of the gateelectrode GE described later, the device becomes more likely to beaffected by the potential of the drain electrode DE. This may result ina reduction of the breakdown voltage. Further, the impurity in thebarrier layer BA may cause the Coulomb scattering in the channel layerCH. This may result in a reduction of the mobility of electrons. Thus,the dope amount of the impurity into the barrier layer BA is preferably1×10¹⁷ (1E17) cm⁻³ or less. Further, it is more preferable to use anondoped barrier layer BA.

Further, as the channel layer CH, there is used a GaN layer, and as thebarrier layer BA, there is used an AlGaN layer. Thus, when the latticeconstants of the layers are different, the film thickness of the barrierlayer BA is required to be equal to, or smaller than the critical filmthickness from which dislocation increases.

Further, as described previously, as the barrier layer BA, it isnecessary to use a nitride semiconductor smaller in electron affinitythan the channel layer CH. However, when a barrier layer BA of amultilayer structure is used, the multilayer may include therein a layerlarger in electron affinity than the channel layer CH. It is essentialonly that at least one layer or more is a layer smaller in electronaffinity than the channel layer CH.

As the cap layer CP, there can be used, for example, a GaN layer. Thethickness of the GaN layer is, for example, about 2 nm. Alternatively,as the cap layer CP, other than GaN, there can be used an AlN layer, anInN layer, or the like. Alternatively, there may also be used a mixedcrystal of the nitride semiconductors (e.g., AlGaN or InAlN). Stillalternatively, the cap layer CP may be omitted.

Further, for the cap layer CP, it is necessary to use a nitridesemiconductor larger in electron affinity than the barrier layer BA.Further, as the cap layer CP, a nondoped layer may be used, or animpurity may be appropriately doped according to the use. As the dopingimpurity, there can be used an n type impurity or a p type impurity.Examples of the n type impurity may include Si, S, and Se. Examples ofthe p type impurity may include Be, C, and Mg.

Whereas, as the channel base layer UC, there is used an AlGaN layer. Asthe cap layer CP, there is used a GaN layer. Thus, when the latticeconstants of the layers are different, the film thickness of the caplayer CP is required to be equal to, or smaller than the critical filmthickness from which dislocation increases.

As the insulation film IF1, there can be used, for example, a siliconnitride film. The thickness of the silicon nitride film is, for example,about 100 nm. Alternatively, there may be used an insulation film otherthan a silicon nitride film. Alternatively, there may be adopted alamination structure of several kinds of insulation films. The materialand the thickness of the insulation film IF1 can be appropriatelyselected according to the use of the semiconductor device. As theinsulation film IF1, preferable is a film larger in bandgap, and smallerin electron affinity than the underlying nitride semiconductor. As thefilm satisfying such conditions, mention may be made of, other than asilicon nitride film (SiN), a silicon oxide (SiO₂) film, a siliconoxynitride film, a silicon oxycarbide (SiOC) film, an aluminum oxide(Al₂O₃ or alumina) film, a hafnium oxide (HfO₂) film, a zirconium oxide(ZrO₂) film, or the like. Further, various organic films satisfy theconditions described above. Further, out of these, it is preferable toselect a film low in interface state density formed at the interfacewith the underlying nitride semiconductor for current collapsesuppression.

The gate electrode GE is formed in the inside of the trench (alsoreferred to as a recess) T penetrating through the insulation film IF1,the cap layer CP, and the barrier layer BA, and dug into some point ofthe channel layer CH via the gate insulation film GI.

As the gate insulation film GI, there can be used an aluminum oxide(Al₂O₃) film. The thickness of the aluminum oxide film is, for example,about 50 nm. As the gate insulation film GI, there may be used aninsulation film other than an aluminum oxide film. Alternatively, theremay be adopted a lamination structure of several kinds of insulationfilms. The material and the thickness of the gate insulation film GI canbe appropriately selected according to the use of the semiconductordevice. As the gate insulation film GI, preferable is a film larger inbandgap, and smaller in electron affinity than the underlying nitridesemiconductor. As films satisfying such conditions, mention may be madeof, other than an aluminum oxide film, a silicon oxide (SiO₂) film, asilicon nitride film (SiN), a hafnium oxide (HfO₂) film, a zirconiumoxide (ZrO₂) film, and the like. The gate insulation film GI affects thevoltage applicable to the gate electrode GE, and the threshold voltage,and hence, is preferably set in consideration of the insulationbreakdown voltage, the dielectric constant, and the film thickness.

As the gate electrode GE, there can be used a titanium nitride (TiN)film. The thickness of the titanium nitride film is, for example, about200 nm. As the gate electrode GE, there may be used a conductive filmother than a titanium nitride film. There may be used a polycrystalsilicon film doped with an impurity such as boron (B) or phosphorus (P).Alternatively, there may be used a metal including Ti, Al, Ni, Au, orthe like. Still alternatively, there may be used a compound film (metalsilicide film) of a metal including Ti, Al, Ni, Au, or the like, and Si.Further alternatively, there may be used a nitride of a metal filmincluding Ti, Al, Ni, Au, or the like. Alternatively, there may beadopted a lamination structure of several kinds of conductive films. Thematerial and the thickness of the gate electrode GE can be appropriatelyselected according to the use of the semiconductor device.

Further, as the gate electrode GE, it is preferable to select a materialless likely to react with the underlying film (e.g., the gate insulationfilm GI), and the overlying film (e.g., the interlayer insulation filmIL1).

Herein, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Theinactivated region IR is an ion implanted region of an inactivatingelement implanted into the lamination part of the potential fixed layerVC, the channel base layer UC, the channel layer CH, and the barrierlayer BA situated between the gate electrode GE and the drain electrodeDE. Injection of an inactivating element may desirably be performed inat least the potential fixed layer VC. Other layers (e.g., the channelbase layer UC, the channel layer CH, and the barrier layer BA) are notrequired to contain an inactivating element with a high concentration.Accordingly, in consideration of the implantation energy and the carrydistance of the inactivating element, adjustment may desirably beachieved so that the inactivating element is contained in a desirableamount in the potential fixed layer VC. For example, an inactivatingelement is implanted so that the activation ratio of the p type impurityin the potential fixed layer VC in the inactivated region IR is lowerthan, and is preferably 1/10 or less the activation ratio of a p typeimpurity in the potential fixed layer VC under the source electrode SEnot inactivated. However, an inactivating element may be diffused intothe layer in the vicinity of the potential fixed layer VC. For example,an inactivating element may be diffused into the channel base layer UC,the channel layer CH, and the barrier layer BA. Alternatively, aninactivating element may be diffused into the layers below the potentialfixed layer VC. However, the inactivating element is for inactivatingthe p type impurity, and does not eliminate the two-dimensional electrongas 2DEG.

Over the gate electrode GE, there is arranged an interlayer insulationfilm IL1. The interlayer insulation film IL1 has a through hole TH andcontact holes C1S and C1D.

As the interlayer insulation film IL1, for example, there can be used asilicon oxide film. The thickness of the silicon oxide film is, forexample, about 2000 nm. Alternatively, there may be used an insulationfilm other than a silicon oxide film. Alternatively, there may beadopted a lamination structure of several kinds of insulation films. Thematerial and the thickness of the interlayer insulation film IL1 can beappropriately selected according to the use of the semiconductor device.As the interlayer insulation film IL1, preferable is a film larger inbandgap, and smaller in electron affinity than the underlying nitridesemiconductor. Further, as the interlayer insulation film IL1, it ispreferable to select a material less likely to react with the gateelectrode GE in contact therewith. As films satisfying such conditions,mention may be made of, other than a silicon oxide film, a siliconnitride film, a silicon oxynitride film, an aluminum oxide (Al₂O₃) film,a hafnium oxide (HfO₂) film, a zirconium oxide (ZrO₂) film, and thelike.

Over the interlayer insulation film IL1 including the through hole THand the contact holes C1S and C1D, there is formed a conductive film.Herein, there is formed a lamination film of a TiN film and an Al film.Of the lamination film, the lamination film in the contact hole C1S orC1D serves as the source electrode SE or the drain electrode DE. On theother hand, the lamination film in the through hole TH serves as thecoupling part VIA.

As the source electrode SE and the drain electrode DE, there can be useda lamination film of a TiN film and an Al film thereover. The thicknessof the TiN film is, for example, about 50 nm. The thickness of the Alfilm is, for example, about 1000 nm. As the materials for the sourceelectrode SE and the drain electrode DE, any materials are acceptable solong as they are in ohmic contact with the nitride semiconductor layer(cap layer CP) at the bottom of the contact hole (C1S or C1D).Particularly, when an n type impurity is doped into the nitridesemiconductor layer (cap layer CP) at the bottom of the contact hole(C1S or C1D), or the nitride semiconductor layer below this layer, theohmic contact becomes more likely to be ensured. Accordingly, for thesource electrode SE and the drain electrode DE, selection from a widerange of material group becomes possible. Further, as the materialsforming the source electrode SE and the drain electrode DE, it ispreferable to select a material less likely to react with the interlayerinsulation film IL1 in contact therewith. As the materials forming thesource electrode SE and the drain electrode DE, there may be used ametal film formed of Ti, Al, Mo (molybdenum), Nb (niobium), V(vanadium), or the like. Alternatively, there can be used mixtures(alloys) of the metals, compound films of the metals and Si (metalsilicide films), nitrides of the metals, and the like. Stillalternatively, there may be used lamination films of the materials.

As the coupling part VIA, as with the source electrode SE and the drainelectrode DE described previously, there can be used a lamination filmof a TiN film and an Al film thereover. The thickness of the TiN filmis, for example, about 50 nm. The thickness of the Al film is, forexample, about 1000 nm. As the materials for the coupling part VIA, anymaterials are acceptable so long as they are in ohmic contact with thenitride semiconductor layer (potential fixed layer VC) at the bottom ofthe through hole TH. Whereas, as the materials forming the coupling partVIA, it is preferable to select a material less likely to react with theinterlayer insulation film IL1 in contact therewith.

For example, when the potential fixed layer VC contains a p typeimpurity, as the materials forming the coupling part VIA, there arepreferably used metal films formed of Ti, Ni, Pt (platinum), Rh(rhodium), Pd (palladium), Ir (iridium), Cu (copper), Ag (silver), andthe like, mixtures (alloys) of the metals, compound films of the metalsand Si (metal silicide films), nitrides of the metals, and the like.Alternatively, there may be used lamination films of the materials.

Further, in the present embodiment, the bottom surface of the throughhole TH is arranged at some point of the potential fixed layer VC. Inthe inside of the through hole TH, there is arranged the coupling partVIA. Thus, it is essential only that the coupling part VIA is arrangedin such a manner as to be in contact with the potential fixed layer VC.For example, the following configuration is also acceptable: the bottomsurface of the through hole TH is arranged at the top surface of thepotential fixed layer VC, so that the bottom of the coupling part VIA isin contact with the potential fixed layer VC. Alternatively, thefollowing configuration is also acceptable: the bottom surface of thethrough hole TH is arranged below the bottom surface of the potentialfixed layer VC, so that a part of the side surface of the coupling partVIA is in contact with the potential fixed layer VC. For example, thebottom surface of the through hole TH may be situated at the surface ofthe buffer layer BU or at some point of the buffer layer BU. The bottomsurface of the through hole TH may be situated at the surface of thenucleation layer NUC or at some point of the nucleation layer NUC.Alternatively, the bottom surface of the through hole TH may be situatedat the surface of the substrate S or at some point of the substrate S.However, the contact between a part of the side surface of the couplingpart VIA and the potential fixed layer VC may result in a smallercontact area. For this reason, the bottom surface of the through hole THis preferably arranged at or below the top surface of the potentialfixed layer VC, and above the lower surface of the potential fixed layerVC.

As described previously, the source pad SP and the drain pad DP areformed integrally with the source electrode SE and the drain electrodeDE, respectively. Accordingly, the source pad SP and the drain pad DPare formed of the same materials as those for the source electrode SEand the drain electrode DE, respectively. Under the source pad SP, thereis arranged the coupling part VIA (FIG. 4).

As the protective film PRO, there can be used an insulation film such asa silicon oxynitride (SiON) film.

[Manufacturing Method Description]

Then, with reference to FIGS. 5 to 25, a description will be given to amethod for manufacturing the semiconductor device of the presentembodiment. In addition, the configuration of the semiconductor devicewill be made clearer. FIGS. 5 to 25 are each a cross sectional view or aplan view showing the semiconductor device of the present embodimentduring a manufacturing step.

As shown in FIG. 5, over a substrate S, there are sequentially formed anucleation layer NUC and a buffer layer BU. As the substrate S, there isused, for example, a semiconductor substrate formed of silicon (Si) witha (111)-plane exposed. Thereover, as the nucleation layer NUC, forexample, an aluminum nitride (AlN) layer is epitaxially grown with afilm thickness of about 200 nm using MOCVD: Metal Organic Chemical VaporDeposition method, or the like

Incidentally, as the substrate S, there may be used a substrate formedof SiC, sapphire, or the like other than the silicon. Further,generally, the nucleation layer NUS, and the nitride semiconductorlayers (III-V group compound layers) subsequent to the nucleation layerNUS are all formed by III-group element plane growth (namely, in thepresent case, gallium plane growth or aluminum plane growth).

Then, over the nucleation layer NUC, as the buffer layer BU, there isformed a superlattice structure in which lamination films (AlN/GaNfilms) each of a gallium nitride (GaN) layer and an aluminum nitride(AlN) layer are repeatedly deposited. For example, gallium nitride (GaN)layers each with a film thickness of about 20 nm and aluminum nitride(AlN) layers each with a film thickness of about 5 nm are alternatelyepitaxially grown using the metal organic chemical vapor depositionmethod or the like. For example, there are formed 40 layers of thelamination films. When the lamination film is grown, the lamination filmmay be grown while being doped with carbon (C). Carbon is doped so thatthe carbon concentration in the lamination film is, for example, about1×10¹⁹ (1E19) cm⁻³.

Further, over the buffer layer BU, as apart of the buffer layer BU, forexample, an AlGaN layer may be epitaxially grown using the metal organicchemical vapor deposition method or the like.

Then, over the buffer layer BU, as the potential fixed layer VC, forexample, a gallium nitride layer (p-GaN layer) containing a p typeimpurity is epitaxially grown using the metal organic chemical vapordeposition method, or the like. For example, as a p type impurity, thereis used magnesium (Mg). For example, a gallium nitride layer isdeposited about 200 nm thick while being doped with magnesium (Mg). TheMg concentration in the deposited film is set at, for example, about5×10¹⁸ (5E18) cm⁻³.

Then, over the potential fixed layer VC, there is formed a channel baselayer UC. Over the potential fixed layer VC, as the channel base layerUC, for example, an AlGaN layer is epitaxially grown using the metalorganic chemical vapor deposition method, or the like. At this step,growth is achieved without performing intentional impurity doping. Thethickness is set at, for example, 1000 nm, and the composition of Al isset at about 3%.

Then, over the channel base layer UC, there is formed a channel layerCH. For example, over the channel base layer UC, a gallium nitride layer(GaN layer) is epitaxially grown using the metal organic chemical vapordeposition method, or the like. At this step, growth is achieved withoutperforming intentional impurity doping. The film thickness of thechannel layer CH is, for example, about 80 nm.

Then, over the channel layer CH, as the barrier layer BA, for example,an AlGaN layer is epitaxially grown using the metal organic chemicalvapor deposition method, or the like. For example, by setting thecomposition ratio of Al at 0.2, and the composition ratio of Ga at 0.8,there is formed an Al_(0.2)Ga_(0.8)N layer. The composition ratio of Alof the AlGaN layer of the barrier layer BA is set larger than thecomposition ratio of Al of the AlGaN layer of the buffer layer BUdescribed previously.

In this manner, there is formed a laminate of the channel base layer UC,the channel layer CH, and the barrier layer BA. Of the laminate, atwo-dimensional electron gas (2DEG) is formed in the vicinity of theinterface between the channel layer CH and the barrier layer BA.

Then, over the barrier layer BA, there is formed a cap layer CP. Forexample, over the barrier layer BA, a gallium nitride layer (GaN layer)is epitaxially grown using the metal organic chemical vapor depositionmethod, or the like. At this step, growth is achieved without performingintentional impurity doping. The film thickness of the cap layer CP is,for example, about 2 nm.

Then, after completion of deposition of the GaN type semiconductor filmsuch as a gallium nitride layer (GaN layer), a heat treatment isperformed in order to activate a p type impurity. For example, a heattreatment is performed at 750° C. for 30 minutes in a nitrogenatmosphere.

Then, as shown in FIGS. 6 and 7, over the cap layer CP, as theinsulation film IF1, a silicon nitride film is deposited with a filmthickness of, for example, about 100 nm using a sputtering method, orthe like.

Then, by a photolithography treatment, a photoresist film PR1 foropening an element isolation region therein is formed over theinsulation film IF1. Then, using the photoresist film PR1 as a mask,nitrogen ions are implanted, thereby to form an isolation region ISO.Thus, ion species such as nitrogen (N) or boron (B) is implanted, sothat the crystal state is changed, resulting in an increase inresistance.

For example, nitrogen ions are implanted at a density of about 5×10¹⁴(5E14) cm⁻² via the insulation film IF1 into a laminate formed of thechannel base layer UC, the channel layer CH, and the barrier layer BA.The implantation energy is, for example, about 120 keV. Incidentally,the nitrogen ion implantation conditions are adjusted so that the depthof implantation, namely, the bottom of the isolation region ISO issituated below the bottom surface of the channel layer CH, and situatedabove the bottom surface of the potential fixed layer VC. Incidentally,the bottom of the isolation region ISO is situated above the bottom ofthe through hole TH (coupling part VIA) described later. In this manner,there is formed the isolation region ISO. The region surrounded by theisolation regions ISO serves as an active region AC. As shown in FIG. 8,the active region AC is, for example, in a substantially rectangularshape having long sides in the X direction. Then, the photoresist filmPR1 is removed by a plasma ashing treatment, or the like.

Then, as shown in FIGS. 9 to 11, using a photolithography technology andan etching technology, the insulation film IF1 is patterned. Forexample, over the insulation film IF1, there is formed a photoresistfilm (not shown). By a photolithography treatment, there is removed thephotoresist film (not shown) in the gate electrode formation region. Inother words, over the insulation film IF1, there is formed a photoresistfilm (not shown) having an opening in the gate electrode formationregion. Then, using the photoresist film (not shown) as a mask, theinsulation film IF1 is etched. When a silicon nitride film is used asthe insulation film IF1, there is performed dry etching using a dryetching gas including a fluorine type gas such as SF₆. Then, by a plasmaashing treatment, or the like, there is removed the photoresist film(not shown). In this manner, over the cap layer CP, there is formed theinsulation film IF1 having an opening in the gate electrode formationregion.

Then, using the insulation film IF1 as a mask, the cap layer CP, thebarrier layer BA, and the channel layer CH are dry etched. As a result,there is formed a trench T penetrating through the cap layer CP and thebarrier layer BA, and reaching some point of the channel layer CH. Asthe etching gas, there is used a dry etching gas including a chlorinetype gas such as BCl₃. At this step, in the isolation region ISO, thereis formed a trench GLT for the gate line GL (FIGS. 10 and 11).

Then, as shown in FIGS. 12 to 14, over the insulation film IF1 includingthe inside of the trench T, a gate electrode GE is formed via a gateinsulation film GI. For example, over the insulation film IF1 includingthe inside of the trench T, as the gate insulation film GI, an aluminumoxide film is deposited with a film thickness of about 50 nm using anALD (Atomic Layer Deposition) method, or the like.

As the gate insulation film GI, other than an aluminum oxide film, theremay be used a silicon oxide film, or a high dielectric constant filmhigher in dielectric constant than a silicon oxide film. As a highdielectric constant film, there may be used a SiN film (siliconnitride), or a hafnium type insulation film such as a HfO₂ film (hafniumoxide film), a hafnium aluminate film, a HfON film (hafnium oxynitridefilm), a HfSiO film (hafnium silicate film), a HfSiON film (hafniumsilicon oxynitride film), or a HfAlO film.

Then, for example, over the gate insulation film GI, as a conductivefilm, for example, a TiN (titanium nitride) film is deposited with afilm thickness of about 200 nm using a sputtering method, or the like.Then, using a photolithography technology, a photoresist film PR2 isformed in the gate electrode formation region. Using the photoresistfilm PR2 as a mask, the TiN film is etched. As a result, there is formeda gate electrode GE. During the etching, the aluminum oxide filmunderlying the TiN film may be etched. For example, during processing ofthe TiN film, there is performed dry etching using a dry etching gascontaining a chlorine type gas such as Cl₂. During processing of thealuminum oxide film, there is performed dry etching using a dry etchinggas containing a chlorine type gas such as BCl₃.

Further, during the etching, the gate electrode GE is patterned in ashape protruding in one direction (toward the right side in FIG. 12, orthe drain electrode DE side). The protrusion part is referred to as afield plate electrode part. The field plate electrode part is a regionof a part of the gate electrode GE extending from the end of the trenchT on the drain electrode DE side toward the drain electrode DE side.

Then, as shown in FIGS. 15 to 17, an inactivating element is implantedinto the potential fixed layer VC on one side (the right side in FIG.15, or the drain electrode side) of the gate electrode GE. As a result,there is formed an inactivated region IR. Incidentally, herein, inconsideration of diffusion of the inactivating element, there is shownthe state in which an inactivating element is implanted into thelamination part of the potential fixed layer VC, the channel base layerUC, the channel layer CH, and the barrier layer BA situated on one sideof the gate electrode GE. Incidentally, in FIG. 15, the end of theregion in which the inactivating element has been implanted is angular.However, for example, as shown in FIG. 1, the end of the region in whichthe inactivating element has been implanted may be in an R (a curvedsurface) shape (the same also applies to other embodiments).

For example, over the gate electrode GE and the insulation film IF1,there is formed a photoresist film PR3. Using a photolithographytechnology, there is removed the photoresist film PR3 over theinsulation film IF1 situated on one side of the gate electrode GE. Usingthe photoresist film PR3 as a mask, an inactivating element isimplanted. As the inactivating element, hydrogen (H) is ion implanted,for example, at a density of 5E14 (5×10¹⁴/cm²), and an energy of 120KeV. It is essential only that implantation of the inactivating elementis performed in at least the potential fixed layer VC. Other layers(e.g., the channel base layer UC, the channel layer CH, and the barrierlayer BA) are not required to contain an inactivating element at a highconcentration. Accordingly, in consideration of the implantation energyand the carry distance of the inactivating element, the implantationconditions may be desirably adjusted so that an inactivating element iscontained in a desirable amount in the potential fixed layer VC. Forexample, an inactivating element is implanted so that the activationratio of the p type element in the potential fixed layer VC in theinactivated region IR is lower than, and is preferably 1/10 or less theactivation ratio of the p type impurity in the potential fixed layer VCunder the source electrode SE not inactivated. Incidentally, a heattreatment may be performed in order to diffuse the ion-implantedinactivating element. However, when a high-temperature heat treatment isperformed, the implanted inactivating element desorbs from the inside ofthe crystal. For this reason, 600° C. or less is preferable.

Herein, as the introducing means of an inactivating element, the ionimplantation method was used. However, there may be performed a plasmatreatment of an inactivating element described in details in SecondEmbodiment.

Then, as shown in FIGS. 18 and 19, over the insulation film IF1including over the gate electrode GE, as the interlayer insulation filmIL1, for example, a silicon oxide film is deposited about 2000 nm inthickness using a sputtering method, or the like.

Then, as shown in FIGS. 20 to 22, using a photolithography technologyand an etching technology, contact holes C1S and C1D, and a through holeTH are formed in the interlayer insulation film IL1 and the insulationfilm IF1. The contact holes C1S and C1D are formed in the sourceelectrode formation region and the drain electrode formation region,respectively. Whereas, the through hole TH is formed in the source padformation region.

For example, over the interlayer insulation film IL1, there is formed afirst photoresist film having openings in a source electrode couplingregion and a drain electrode coupling region, respectively. Then, usingthe first photoresist film as a mask, the interlayer insulation film IL1and the insulation film IF1 are etched. As a result, there are formedthe contact holes C1S and C1D.

When a silicon oxide film is used as the interlayer insulation film IL1,and a silicon nitride film is used as the insulation film IF1, dryetching using a dry etching gas containing a fluorine type gas such asSF₆ is performed for etching of the films.

Then, after removing the first photoresist film, over the interlayerinsulation film IL1 including the insides of the contact holes C1S andC1D, there is formed a second photoresist film having an opening in athrough hole formation region. Then, using the second photoresist filmas a mask, the interlayer insulation film IL1, the insulation film IF1,the isolation region ISO, the channel base layer UC, and the potentialfixed layer VC are partially etched. As a result, there is formed athrough hole TH. In other words, there is formed a through hole THpenetrating through the interlayer insulation film IL1, the insulationfilm IF1, the isolation region ISO, and the channel base layer UC, andreaching some point of the potential fixed layer VC.

As described previously, etching is performed so that the bottom of thethrough hole TH is in the potential fixed layer VC, and is situatedbelow the bottom of the isolation region ISO.

When a silicon oxide film is used as the interlayer insulation film IL1,and a silicon nitride film is used as the insulation film IF1, first,the films are removed by dry etching using a dry etching gas containinga fluorine type gas such as SF₆. Then, the isolation region ISO, thechannel base layer (AlGaN layer) UC, and in the middle of the potentialfixed layer (pGaN layer) VC are removed by dry etching using a dryetching gas containing a chlorine type gas such as BCl₃.

Incidentally, the formation order of the contact holes C1S and C1D, andthe through hole TH is not limited to that described above. After theformation of the through hole TH, the contact holes C1S and C1D may beformed. Alternatively, the following is also acceptable: the interlayerinsulation film IL1 in the through hole formation region, the sourceelectrode coupling region, and the drain electrode coupling region isremoved; then, the insulation film IF1, the isolation region ISO, thechannel base layer UC, and the potential fixed layer VC in the throughhole formation region are removed partway; further, the insulation filmIF1 in the source electrode coupling region and the drain electrodecoupling region is removed. Thus, the formation steps of the contactholes C1S and C1D, and the through hole TH may assume various steps.

From the bottom surfaces of the contact holes C1S and C1D formed in thesteps described above, there is exposed the cap layer CP. From thebottom surface of the through hole TH, there is exposed the potentialfixed layer VC.

Then, as shown in FIGS. 23 to 25, over the cap layer CP on the oppositesides of the gate electrode GE, there are formed the source electrode SEand the drain electrode DE. Further, at the end of the source electrodeSE, there is formed a source pad SP, and at the end of the drainelectrode DE, there is formed a drain pad DP (FIG. 22).

For example, over the interlayer insulation film IL1 including theinsides of the contact holes C1S and C1D, and the through hole TH, thereis formed a conductive film. For example, as a conductive film, alamination film (Al/TiN) formed of a titanium nitride (TiN) film and analuminum (Al) film thereover is formed using a sputtering method, or thelike. The titanium nitride film has a film thickness of, for example,about 50 nm. The aluminum film has a film thickness of, for example,about 1000 nm.

Then, using a photolithography technology, a photoresist film (notshown) is formed in the formation region of the source electrode SE, thedrain electrode DE, the source pad SP, and the drain pad DP. Using thephotoresist film (not shown) as a mask, the conductive film (Al/TiN) isetched. There is performed dry etching using a dry etching gascontaining a chlorine type gas such as BCl₃. By this step, there isformed a coupling part VIA in which the conductive film is embedded inthe through hole TH; and there are formed the source electrode SE, thedrain electrode DE, the source pad SP, and the drain pad DP. Each planarshape of the source electrode SE and the drain electrode DE is arectangular shape (line shape) having long sides in the Y direction asshown in FIG. 25. Whereas, each planar shape of the source pad SP andthe drain pad DP is a rectangular shape (line shape) having long sidesin the X direction. The source pad SP is arranged in such a manner as toensure a coupling among a plurality of source electrodes SE. The drainpad DP is arranged in such a manner as to ensure a coupling among aplurality of drain electrodes DE.

Then, under the source pad SP, the through hole TH is situated, so thatthe source pad SP and the potential fixed layer VC are electricallycoupled with each other via the coupling part VIA (FIG. 24).

Then, over the interlayer insulation film IL1 including over the sourceelectrode SE, the drain electrode DE, the source pad SP, and the drainpad DP, there is formed a protective film (also referred to as aninsulation film, a covering film, or a surface protective film) PRO. Forexample, over the interlayer insulation film IL1, as the protective filmPRO, for example, a silicon oxynitride (SiON) film is deposited using asputtering method, or the like (see FIGS. 3 and 4).

By the steps up to this point, there can be formed a semiconductordevice of the present embodiment. Incidentally, the steps describedabove are examples. The semiconductor device of the present embodimentmay also be manufactured by other steps than the steps described above.For example, after performing the ion implantation of an inactivatingelement, the gate electrode GE may be formed.

Thus, in accordance with the present embodiment, the potential fixedlayer VC which is a conductive layer is provided between the bufferlayer BU and the channel layer CH, and is coupled with the sourceelectrode SE. This can reduce the characteristic fluctuations of thesemiconductor device. Namely, the potential fixed layer VC can prevent achange in potential due to a change in charge amount of the layers belowthis layer (e.g., the buffer layer BU) from affecting even the channellayer CH. This can reduce the fluctuations in characteristics such asthe threshold potential and the ON resistance.

Further, in the present embodiment, as the potential fixed layer VC,there is used a p type nitride semiconductor layer. Accordingly, whenthe drain electrode DE is applied with a positive potential (positivebias), the potential fixed layer VC is depleted, resulting in a highresistance layer. This can suppress the deterioration of, or can improvethe drain breakdown voltage.

Further, in the present embodiment, the coupling part VIA in the throughhole TH is arranged in the isolation region ISO outside the activeregion AC in which electrons are conducted, and under the formationregion of the source pad SP. As a result, it is possible to implementminiaturization and high integration of semiconductor devices. Further,it is possible to ensure a large active region AC in which electrons canbe conducted. For this reason, it is possible to reduce the ONresistance per unit area.

For example, when an impurity such as Fe is doped into the buffer layerfor achieving a higher breakdown voltage (see Patent Document 1), the Feforms a deep level. Such a deep level serves as the base point fortrapping and release of electrons or holes during the operation of asemiconductor device, and hence causes the fluctuations incharacteristics such as the threshold potential. Particularly, when thelevel is deep, the deep level may cause fluctuations in characteristicssuch as the threshold potential during a period as very long as severalminutes to several days according to the energy depth or position.

In contrast, in the present embodiment, the potential fixed layer VCwhich is a conductive layer is provided between the buffer layer BU andthe channel layer CH, and is coupled with the source electrode SE. Thiscan reduce the characteristic fluctuations of the semiconductor device.

Whereas, when a superlattice structure is used as the buffer layer BU,the superlattice structure becomes a very deep quantum well (a very highbarrier against the movement of electrons or holes). For this reason,when electric charges such as electrons or holes are trapped in thevicinity of the superlattice structure, it becomes difficult for theelectric charges to move in the vertical direction to the substrate.Accordingly, when a superlattice structure is used, unnecessary electriccharges are difficult to remove. This may cause fluctuations incharacteristics such as the threshold potential during a very longperiod.

In contrast, in the present embodiment, the potential fixed layer VCwhich is a conductive layer is provided between the buffer layer BU andthe channel layer CH, and is coupled with the source electrode SE. Thiscan reduce the characteristic fluctuations of the semiconductor device.

Further, when a plasma treatment is performed during the manufacturingsteps, electric charges tend to be introduced into the semiconductorlayer. Examples of the plasma treatment include PECVD, and the plasmaasking treatment of a photoresist film. The electric charges introducedduring such a treatment may cause fluctuations in characteristics suchas the threshold potential. Particularly, a nitride semiconductor has alarge bandgap, and also a high insulation property. For this reason, theelectric charges introduced by a plasma treatment, or the like are lesslikely to be drained. This may also cause fluctuations incharacteristics such as the threshold potential during a very longperiod.

In contrast, in the present embodiment, the potential fixed layer VCwhich is a conductive layer is provided between the buffer layer BU andthe channel layer CH, and is coupled with the source electrode SE. Thiscan reduce the characteristic fluctuations of the semiconductor device.

Further, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Thus, thepotential fixed layer VC situated between the gate electrode GE and thedrain electrode DE is inactivated, resulting in the inactivated regionIR. This can improve the drain breakdown voltage.

FIG. 26 is a graph showing the relationship between the longitudinaldrain breakdown voltage and the concentration of the activated acceptorin the potential fixed layer. The graph shows the results of simplecalculation of the dependency of the activated acceptor concentration inthe potential fixed layer with respect to the longitudinal drainbreakdown voltage. Incidentally, the actual breakdown voltage differsdepending upon the epitaxial structure other than that of the potentialfixed layer. The horizontal axis denotes the acceptor concentration[cm⁻³], and the vertical axis denotes the drain breakdown voltage [V].As shown in FIG. 26, when the thickness of the potential fixed layer isset constant, the drain breakdown voltage decreases with an increase inacceptor concentration in the potential fixed layer. Namely, even whenthe thickness of the potential fixed layer is any of 2.0 μm, 1.0 μm, 0.5μm, 0.2 μm, and 0.1 μm, with an increase in acceptor concentration, thedrain breakdown voltage decreases. Particularly, when the acceptorconcentration exceeds 1×10¹⁷ (1E17) cm⁻³, the drain breakdown voltage isremarkably deteriorated. Accordingly, from the viewpoint of the drainbreakdown voltage, a restriction is caused on the concentration of the ptype impurity in the potential fixed layer.

Particularly, the epitaxial growth layer of a nitride semiconductor suchas GaN has a dislocation/defect. For this reason, even when a p typeimpurity (acceptor) is introduced, the generation rate of electriccharges (herein, holes) is as low as less than 10%. Thus, doping of a ptype impurity (acceptor) enough to remove the electric chargesaccumulated in the substrate causes the deterioration of the drainbreakdown voltage.

In contrast, in the present embodiment, while keeping the concentrationof the p type impurity high on the source electrode SE side, the p typeimpurity can be inactivated on the drain electrode DE side. Thus, the ptype potential fixed layer in a region affecting the drain breakdownvoltage can be inactivated. Accordingly, it becomes possible to set highthe p type impurity concentration (acceptor concentration) on the sourceelectrode SE side independent of the breakdown voltage. For this reason,while keeping the breakdown voltage on the drain side, the electriccharges such as electrons or holes are removed. This can suppress thefluctuations in characteristics such as the threshold potential.

Particularly, as described previously, when a p type nitridesemiconductor layer is used as the potential fixed layer, with the drainelectrode DE applied with a positive potential (positive bias), thepotential fixed layer VC is depleted, resulting in a high resistancelayer. For this reason, the conductivity type of the impurity in thepotential fixed layer is more preferably set as a p type. Further, asthe p type impurity, Mg is useful. As the inactivating element forreducing the activation ratio of Mg, H is preferable. Particularly, Hhas a small atomic weight, and hence can be implanted even into a deeplayer with ease, and is preferably used as an inactivating element.

Further, it is possible to individually control the p type impurityconcentration (acceptor concentration) on the drain electrode DE side,and the p type impurity concentration (acceptor concentration) on thesource electrode SE side. For this reason, it becomes possible toincrease the film thickness of the p type potential fixed layer VC. Thiscan reduce the coupling resistance between the p type potential fixedlayer VC and the coupling part VIA. Further, it is possible to increasethe process margin when the through hole TH in which the coupling partVIA is embedded is formed by etching.

Applied Example 1

In the semiconductor device (see FIG. 3), the end of the inactivatedregion IR on the gate electrode GE side is not limited to the positionshown in the semiconductor device (see FIG. 3), and can be appropriatelychanged between the gate electrode GE and the drain electrode DE.

FIG. 27 is a cross sectional view showing a configuration of asemiconductor device of Applied Example 1 of the present embodiment. Theconfiguration is the same as that of the semiconductor device (FIGS. 2to 25) except for the position of the end of the inactivated region IRon the gate electrode GE side.

As shown in FIG. 27, the end of the inactivated region IR on the gateelectrode GE side may be allowed to correspond to the end of the trenchT on the drain electrode DE side. Namely, in this case, the inactivatedregion IR extends from the end of the trench T on the drain electrode DEside to under the drain electrode DE.

Applied Example 2

FIG. 28 is a cross sectional view showing a configuration of asemiconductor device of Applied Example 2 of the present embodiment. Theconfiguration is the same as that of the semiconductor device (FIGS. 2to 25) except for the position of the end of the inactivated region IRon the gate electrode GE side.

As shown in FIG. 28, the end of the inactivated region IR on the gateelectrode GE side may be arranged between the end on the gate electrodeGE and the drain electrode DE. Namely, in this case, the inactivatedregion IR extends from the position distant from the end of the gateelectrode GE on the drain electrode DE side by a given distance to underthe drain electrode DE.

Applied Example 3

In the semiconductor device (see FIG. 1), the coupling part VIA isprovided; and the potential fixed layer VC is coupled with the sourceelectrode SE via the coupling part VIA. However, the formation of thecoupling part VIA may be omitted.

FIG. 29 is a cross sectional view schematically showing a configurationof a semiconductor device of Applied Example 3 of the presentembodiment. In the present applied example, over a substrate S, thereare sequentially formed a nucleation layer NUC, a buffer layer BU, a ptype potential fixed layer VC, a channel base layer UC, a channel layerCH, and a barrier layer BA. On the channel layer CH side in the vicinityof the interface between the channel layer CH and the barrier layer BA,there is formed a two-dimensional electron gas (2DEG). Whereas, when thegate electrode GE is applied with a positive potential (thresholdpotential), a channel is formed in the vicinity of the interface betweenthe gate insulation film GI and the channel layer CH. Thus, although thep type potential fixed layer VC is provided, the p type potential fixedlayer VC is not fixed to the source potential. Thus, the p typepotential fixed layer VC is arranged below the channel layer CH. Onlythis can reduce the effect of the electric charges such as electrons orholes on the gate electrode source end most affecting the thresholdpotential. This can suppress the fluctuations in characteristics such asthe threshold potential. However, fixing of the potential of the p typepotential fixed layer VC results in a higher effective p type impurityconcentration (acceptor concentration). As a result, the electric chargeremoving effect is enhanced.

Accordingly, even when the coupling part VIA is not provided, whilesetting high the p type impurity concentration (acceptor concentration)of the potential fixed layer VC on the source electrode SE side, the ptype impurity of the potential fixed layer VC is inactivated on thedrain electrode DE side. As a result, while keeping the electric chargeremoving effect, the breakdown voltage on the drain side can beimproved.

Second Embodiment

In First Embodiment, using the photoresist film as a mask, aninactivating element was implanted. However, using the gate insulationfilm GI as a mask, an inactivating element may be implanted.

[Structure Description]

FIG. 30 is a cross sectional view schematically showing a configurationof a semiconductor device of the present embodiment. Incidentally, theconfiguration of the present embodiment is the same as that in FirstEmbodiment, except for the configuration of the gate insulation film GI.For this reason, a detailed description on the same configuration willbe omitted.

In the semiconductor device of the present embodiment, as with FirstEmbodiment (FIG. 1), over a substrate S, there are sequentially formed anucleation layer NUC, a buffer layer BU, a potential fixed layer VC, achannel base layer UC, a channel layer CH, and a barrier layer BA.

A MISFET of the present embodiment has, as with First Embodiment (FIG.1), a gate electrode GE formed over the channel layer CH via a gateinsulation film GI, and a source electrode SE and a drain electrode DEformed over the barrier layer BA on the opposite sides of the gateelectrode GE, respectively. The MISFET is formed in an active region(AC) defined by isolation regions ISO. Further, the gate electrode GE isformed in the inside of a trench T penetrating through the barrier layerBA, and reaching some point of the channel layer CH via the gateinsulation film GI.

Herein, in the present embodiment, in the isolation region ISO, there isprovided a coupling part (also referred to as a via) VIA penetratingthrough the isolation region ISO, and reaching the underlying potentialfixed layer VC. The coupling part VIA is electrically coupled with thesource electrode SE. Thus, the potential fixed layer VC is provided, andcoupled with the source electrode SE. As a result, it is possible toreduce the fluctuations in characteristics such as the thresholdpotential and the ON resistance.

Further, in the present embodiment, the coupling part VIA in the throughhole TH is arranged in the isolation region ISO outside the activeregion AC in which electrons are conducted, and under the formationregion of the source pad SP. As a result, it is possible to implementminiaturization and high integration of semiconductor devices. Further,it is possible to ensure a large active region AC in which electrons canbe conducted. For this reason, it is possible to reduce the ONresistance per unit area.

Further, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Theinactivated region IR is an inactivating element doped region. Thus, thepotential fixed layer VC doped with an impurity to produce a p typesituated between the gate electrode GE and the drain electrode DE isinactivated, resulting in the inactivated region IR. As a result, it ispossible to improve the drain breakdown voltage. The activation ratio ofthe inactivated region IR is preferably set smaller than, and at 1/10 orless the activation ratio of the region under the source electrode SE.

Then, in the present embodiment, the gate insulation film extends fromunder the gate electrode GE to the source electrode SE. Thus, the gateinsulation film GI on the source electrode SE side is left. As a result,the gate insulation film GI can be used as a mask for doping aninactivating element.

Specifically, the inactivated region IR is provided between the gateelectrode GE and the drain electrode DE; and the gate insulation film GIis left in a region between the end of the gate electrode GE on thedrain electrode DE side and the source electrode SE.

With reference to FIGS. 31 and 32, the semiconductor device of thepresent embodiment will be further described in details. FIGS. 31 and 32are each a cross sectional view showing a configuration of thesemiconductor device of the present embodiment.

As shown in FIGS. 31 and 32, in the semiconductor device of the presentembodiment, as with First Embodiment, over a substrate S, there aresequentially formed a nucleation layer NUC, a buffer layer BU, apotential fixed layer VC, a channel base layer UC, a channel layer (alsoreferred to as an electron transit layer) CH, and a barrier layer BA.The nucleation layer NUC is formed of a nitride semiconductor layer. Thebuffer layer BU is formed of a monolayered or multilayered nitridesemiconductor layer doped with an impurity for forming a deep level in anitride semiconductor. Herein, there is used a superlattice structureformed of a multilayer nitride semiconductor layer. The potential fixedlayer VC is formed of a nitride semiconductor layer doped with animpurity, and has a conductivity. The channel base layer UC is formed ofa nitride semiconductor layer smaller in electron affinity than thechannel layer CH, and smaller in average lattice constant in thesubstrate surface direction than the channel layer CH. The channel layerCH is formed of a nitride semiconductor layer larger in electronaffinity than the channel base layer UC. The barrier layer BA is formedof a nitride semiconductor layer smaller in electron affinity than thechannel layer CH, and smaller in electron affinity than the channel baselayer UC.

As the potential fixed layer VC, there can be used, for example, a GaNlayer doped with a p type impurity. Other than the GaN layer, there maybe used an AlN layer or an InN layer. Alternatively, a mixed crystal ofthe nitride semiconductors may be used. For example, as the potentialfixed layer VC, there can be used a GaN layer doped with Mg in an amountof about 5×10¹⁸ (5E18) cm⁻³ as an impurity. The film thickness of thepotential fixed layer VC is about 200 nm.

As the gate insulation film GI, there can be used an aluminum oxide(Al₂O₃) film. The thickness of the aluminum oxide film is, for example,about 50 nm. As the gate insulation film GI, there may be used aninsulation film other than an aluminum oxide film. Alternatively, theremay be adopted a lamination structure of several kinds of insulationfilms.

The inactivated region IR is provided between the gate electrode GE andthe drain electrode DE, and reaches the potential fixed layer VC in thedepth direction. The inactivated region IR is a region resulting frominactivation of the potential fixed layer VC doped with an impurity toproduce a p type situated between the gate electrode GE and the drainelectrode DE by doping of an inactivating element. In the presentembodiment, the inactivated region IR is formed by implanting aninactivating element using the gate insulation film GI as a mask. Forthis reason, in other regions than the formation region of theinactivated region IR, there is left the gate insulation film GI.

Specifically, in a region between the gate electrode GE and the drainelectrode DE, there is provided the inactivated region IR; and in aregion between the end of the gate electrode GE on the drain electrodeDE side and the source electrode SE, there is left the gate insulationfilm GI.

As the gate electrode GE, there can be used a titanium nitride (TiN)film. The thickness of the titanium nitride film is, for example, about200 nm. As the gate electrode GE, there may be used a conductive filmother than a titanium nitride film.

Over the gate electrode GE, there is arranged the interlayer insulationfilm IL1. The interlayer insulation film IL1 has the through hole TH andthe contact holes C1S and C1D. The source pad SP and the drain pad DPare formed integrally with the source electrode SE and the drainelectrode DE, respectively. Accordingly, the source pad SP and the drainpad DP are formed of the same materials as those for the sourceelectrode SE and the drain electrode DE, respectively. Under the sourcepad SP, there is arranged the coupling part VIA (FIG. 4).

As a protective film PRO, there can be used an insulation film such as asilicon oxynitride (SiON) film.

Herein, in the present embodiment, in the isolation region ISO, there isprovided a coupling part (also referred to as a via) VIA penetratingthrough the isolation region ISO, and reaching the underlying potentialfixed layer VC. The coupling part VIA is electrically coupled with thesource electrode SE. Thus, the potential fixed layer VC is provided, andcoupled with the source electrode SE. As a result, as with FirstEmbodiment, it is possible to reduce the fluctuations in characteristicssuch as the threshold potential and the ON resistance.

Further, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Theinactivated region IR is an ion implanted region of an inactivatingelement implanted into the lamination part of the potential fixed layerVC, the channel base layer UC, the channel layer CH, and the barrierlayer BA situated between the gate electrode GE and the drain electrodeDE. Injection of an inactivating element may desirably be performed inat least the potential fixed layer VC. Other layers (e.g., the channelbase layer UC, the channel layer CH, and the barrier layer BA) are notrequired to contain an inactivating element with a high concentration.Accordingly, in consideration of the implantation energy and the carrydistance of the inactivating element, adjustment may desirably beachieved so that an inactivating element is contained in a desirableamount in the potential fixed layer VC. For example, an inactivatingelement is implanted so that the activation ratio of the p type impurityin the potential fixed layer VC in the inactivated region IR is lowerthan, and is preferably 1/10 or less the activation ratio of the p typeimpurity in the potential fixed layer VC under the source electrode SEnot inactivated. However, an inactivating element may be diffused intothe layer in the vicinity of the potential fixed layer VC. For example,an inactivating element may be diffused into the channel base layer UC,the channel layer CH, and the barrier layer BA. Alternatively, aninactivating element may be diffused into the layers below the potentialfixed layer VC. However, the inactivating element is for inactivatingthe p type impurity, and does not eliminate the two-dimensional electrongas 2DEG.

Further, in the present embodiment, the formation is achieved byimplanting an inactivating element using the gate insulation film GI asa mask. Particularly, the aluminum oxide film has a function ofinhibiting the transmission of small ions such as hydrogen (H). For thisreason, use of the gate insulation film (aluminum oxide film) GI as amask can favorably achieve selective implantation of an inactivatingelement.

[Manufacturing Method Description]

Then, with reference to FIGS. 33 to 49, a description will be given to amethod for manufacturing the semiconductor device of the presentembodiment. In addition, the configuration of the semiconductor devicewill be made clearer. FIGS. 33 to 49 are each a cross sectional view ora plan view showing the semiconductor device of the present embodimentduring a manufacturing step. Incidentally, the configuration of thepresent embodiment is the same as that of First Embodiment, except forthe configuration of the gate insulation film GI. Accordingly, the stepsin association with the gate insulation film GI will be described indetails.

As shown in FIGS. 33 and 34, over a substrate S, there are sequentiallyformed a nucleation layer NUC and a buffer layer BU. For these, thematerials described in First Embodiment are used. Thus, the formationcan be achieved in the same manner as in First Embodiment.

Then, over the buffer layer BU, as a potential fixed layer VC, forexample, a gallium nitride layer (p-GaN layer) containing a p typeimpurity is epitaxially grown using the metal organic chemical vapordeposition method, or the like. For example, as a p type impurity, thereis used magnesium (Mg). For example, while doping magnesium (Mg), agallium nitride layer is deposited about 200 nm in thickness. The Mgconcentration in the deposited film is set at, for example, about 5×10¹⁸(5E18) cm⁻³.

Then, over the potential fixed layer VC, there are sequentially formed achannel base layer UC, a channel layer CH, a barrier layer BA, a caplayer CP, and an insulation film IF1. For these, the materials describedin First Embodiment are used. Thus, the formation can be achieved in thesame manner as in First Embodiment. Then, in the same manner as in FirstEmbodiment, there is formed an isolation region ISO. Further, there isformed a trench T penetrating through the insulation film IF1, the caplayer CP, and the barrier layer BA, and reaching some point of thechannel layer CH. At this step, in the isolation region ISO, there isformed a trench GLT for the gate line GL (FIG. 34).

Then, as shown in FIGS. 35 to 37, over the insulation film IF1 includingthe inside of the trench T, as the gate insulation film GI, an aluminumoxide film is deposited with a film thickness of about 50 nm using anALD method, or the like. Further, over the gate insulation film GI, as aconductive film, for example, a TiN (titanium nitride) film is depositedwith a film thickness of about 200 nm using a sputtering method, or thelike.

Then, using a photolithography technology, there is formed a photoresistfilm PR2 having an opening in the formation region of the inactivatedregion IR. Using the photoresist film PR2 as a mask, the TiN film andthe aluminum oxide film are etched. As a result, there is exposed theinsulation film IF1 in the formation region of the inactivated regionIR.

Then, as shown in FIGS. 38 to 40, there is formed a gate electrode GE.The gate electrode GE has the same shape as that of First Embodiment,and has a field plate electrode part. Over a TiN film to be the gateelectrode GE, there is formed a photoresist film PR21. Using aphotolithography technology, the photoresist film PR21 is left only inthe gate electrode formation region. Then, using the photoresist filmPR21 as a mask, the TiN film to be the gate electrode GE is etched,thereby to form the gate electrode GE. Upon the etching, the gateinsulation film (aluminum oxide film) GI underlying the TiN film is notetched, and is left. For processing of the TiN film, there is used a dryetching gas containing a chlorine type gas such as Cl₂.

Then, as shown in FIGS. 41 to 43, using the gate insulation film(aluminum oxide film) GI and the gate electrode GE as a mask, aninactivating element is implanted into the potential fixed layer VC onone side of the gate electrode GE (on the right side in FIG. 41, or thedrain electrode side). As a result, there is formed an inactivatedregion IR. Incidentally, herein, in consideration of diffusion of theinactivating element, there is shown the state in which an inactivatingelement is implanted into the lamination part of the potential fixedlayer VC, the channel base layer UC, the channel layer CH, and thebarrier layer BA situated on one side of the gate electrode GE.

For example, using the gate insulation film (aluminum oxide film) GI andthe gate electrode GE as a mask, an inactivating element is implanted.When an inactivating element is implanted using the gate insulation film(aluminum oxide film) GI and the gate electrode GE as a mask, there isperformed a plasma treatment of hydrogen (H) as an inactivating element.Specifically, for example, there is a method of exposure into theatmosphere converted into a plasma by an electronic cyclotron resonance(ECR) method. An inactivating element is implanted so that theactivation ratio of the p type impurity in the potential fixed layer VCin the inactivated region IR is lower than, and is preferably 1/10 orless the activation ratio of the p type impurity in the potential fixedlayer VC under the source electrode SE not inactivated.

For the gate insulation film GI, a dense film is often used. Using thegate insulation film GI as a mask, an inactivating element is implanted.This can favorably achieve selective implantation of an inactivatingelement. Particularly, an aluminum oxide can suppress the transmissionof small atoms such as hydrogen (H), and is preferably used as a maskfor inhibiting the implantation of an inactivating element.

Then, as shown in FIGS. 44 to 46, in the same manner as in FirstEmbodiment, over the gate electrode GE, there is formed an interlayerinsulation film IL1. Further, in the interlayer insulation film IL1,there are formed contact holes C1S and C1D, and a through hole TH. Atthis step, in the formation region of the contact hole C1S, and theformation region of the through hole TH, there is left the gateinsulation film (aluminum oxide film) GI. Accordingly, the interlayerinsulation film IL1, the gate insulation film GI, and the insulationfilm IF1 are etched, thereby to form the contact hole C1S (FIG. 44). Theinterlayer insulation film IL1, the gate insulation film GI, theinsulation film IF1, the isolation region ISO, the channel base layerUC, and the potential fixed layer VC are partially etched, thereby toform the through hole TH (FIG. 45).

Then, as shown in FIGS. 47 to 49, in the same manner as in FirstEmbodiment, over the cap layer CP on the opposite sides of the gateelectrode GE, there are formed the source electrode SE, the drainelectrode DE, and the like. Further, over the source electrode SE, thedrain electrode DE, and the like, there is formed a protective film PRO.

By the steps up to this point, it is possible to form the semiconductordevice of the present embodiment. Incidentally, the steps describedabove are examples. The semiconductor device of the present embodimentmay be manufactured by other steps than the steps described above.

Thus, also in the present embodiment, as with First Embodiment, thepotential fixed layer VC is provided, and is coupled with the sourceelectrode SE. Accordingly, it is possible to reduce the characteristicfluctuation of the semiconductor device. Further, also in the presentembodiment, as with First Embodiment, the coupling part VIA in thethrough hole TH is arranged in the isolation region ISO. As a result, itis possible to implement miniaturization and high integration ofsemiconductor devices. Further, it is possible to ensure a large activeregion AC in which electrons can be conducted. For this reason, it ispossible to reduce the ON resistance per unit area.

Further, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Thus, thepotential fixed layer VC situated between the gate electrode GE and thedrain electrode DE is inactivated, resulting in the inactivated regionIR. This can improve the drain breakdown voltage. Further, in thepresent embodiment, using the gate insulation film GI as a mask, theinactivating element was implanted. This can favorably achieve selectiveimplantation of an inactivating element.

Incidentally, the plasma treatment of an inactivating element is atreatment of exposing a substrate in an atmosphere plasma-discharged ina gas containing an inactivating element. For example, a treatmentsubstrate is exposed into an atmosphere plasma-discharged in a gascontaining a hydrogen element. In this case, hydrogen radicals aregenerated, and introduced into a region in which a mask is not formed.The case using such a radical has an advantage of the crystal being lesslikely to be damaged by ion implantation. Further, a high-densityinactivating element can be introduced into the crystal while thecrystal being less damaged. For this reason, the activation ratio of thep type element in the potential fixed layer VC in the inactivated regionIR can be set sufficiently lower than the activation ratio of the p typeimpurity in the potential fixed layer VC under the source electrode SEnot inactivated.

Alternatively, as the plasma treatment of an inactivating element, theremay be used a deposition treatment. For example, in the deposition stepof a silicon nitride film, silane (SiH₄) or ammonia (NH₃) is used as araw material gas. In accordance with plasma CVD using a compound gas ofsuch an inactivating element, the compound gas of an inactivatingelement such as silane or ammonia is decomposed, resulting in radicalsof an inactive element such as hydrogen radicals. An inactivatingelement can also be introduced by such a treatment.

Particularly, with the gate insulation film GI left as a mask describedabove, a silicon nitride film is deposited by a PECVD (plasma-enhancedchemical vapor deposition) method using silane (SiH₄) or ammonia (NH₃)as a raw material gas. As a result, it is possible to perform theintroduction of a hydrogen element and the deposition with a siliconnitride film at the same time. The silicon nitride film can be used as,for example, the lower film of the interlayer insulation film IL1.Namely, over a silicon nitride film, there is formed a silicon oxidefilm. The lamination film thereof forms the interlayer insulation filmIL1. In accordance with the interlayer insulation film IL1 with such aconfiguration, at the time of formation of the contact holes C1S and C1Ddescribed later, a silicon nitride film serves as an etching stopper. Asa result, it is possible to form the contact holes C1S and C1D withprecision.

Third Embodiment

In First and Second Embodiments, the recess gate type semiconductordevices were shown as examples. However, semiconductor devices withother configurations are also acceptable. For example, as in the presentembodiment, there may be used a junction type semiconductor device inwhich a gate junction layer is arranged under a gate electrode.

Below, with reference to the accompanying drawings, a semiconductordevice of the present embodiment will be described in details.

[Structure Description]

FIG. 50 is a cross sectional view schematically showing a configurationof the semiconductor device of the present embodiment. The semiconductordevice (semiconductor element) of the present embodiment is a transistorusing a nitride semiconductor. The semiconductor device can be used as ahigh electron mobility transistor (HEMT) type power transistor.

In the semiconductor device of the present embodiment, as with FirstEmbodiment, over a substrate S, there are sequentially formed anucleation layer NUC, a buffer layer BU, a potential fixed layer VC, achannel base layer UC, a channel layer (also referred to as an electrontransit layer) CH, and a barrier layer BA. The nucleation layer NUC isformed of a nitride semiconductor layer. The buffer layer BU is formedof a single layered or multilayered nitride semiconductor layer dopedwith an impurity for forming a deep level in a nitride semiconductor.Herein, there is used a superlattice structure formed of a multilayernitride semiconductor layer. The potential fixed layer VC is formed of anitride semiconductor layer doped with an impurity to produce a p typewith respect to a nitride semiconductor, and has a conductivity. Thechannel base layer UC is formed of a nitride semiconductor layer smallerin electron affinity than the channel layer CH, and smaller in averagelattice constant in the substrate surface direction than the channellayer CH. The channel layer CH is formed of a nitride semiconductorlayer larger in electron affinity than the channel base layer UC. Thebarrier layer BA is formed of a nitride semiconductor layer smaller inelectron affinity than the channel layer CH, and smaller in electronaffinity than the channel base layer UC.

The semiconductor device of the present embodiment has a gate electrodeGE formed over the barrier layer BA via a gate junction layer JL, and asource electrode SE and a drain electrode DE formed over the barrierlayer BA on the opposite sides of the gate electrode GE. Thesemiconductor device is formed in an active region AC defined by theisolation regions ISO. The gate junction layer JL is doped with a p typeimpurity. Further, the gate junction layer JL and the gate electrode GEare preferably in ohmic contact for positive holes.

On the channel layer CH side in the vicinity of the interface betweenthe channel layer CH and the barrier layer BA, there is formed atwo-dimensional electron gas (2DEG). Whereas, under the gate junctionlayer JL, negative charges resulting from acceptor ionization raise theconduction band of the channel layer CH. Accordingly, a two-dimensionalelectron gas (2DEG) is not formed. For this reason, in the semiconductordevice of the present embodiment, with the gate electrode GE not appliedwith a positive potential (threshold potential), the OFF state can bekept; and with the gate electrode GE applied with a positive potential(threshold potential), the ON state can be kept. Thus, the normally offoperation can be performed.

Herein, in the present embodiment, in the isolation region ISO, there isprovided a coupling part (also referred to as a via) VIA penetratingthrough the isolation region ISO, and reaching the underlying potentialfixed layer VC. The coupling part VIA is electrically coupled with thesource electrode SE. Thus, the potential fixed layer VC is provided, andcoupled with the source electrode SE. As a result, it is possible toreduce the fluctuations in characteristics such as the thresholdpotential and the ON resistance.

Further, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Theinactivated region IR reaches the potential fixed layer VC in the depthdirection. Thus, the potential fixed layer VC doped with an impurity toproduce a p type situated between the gate electrode GE and the drainelectrode DE is inactivated by doping of an inactivating element,resulting in the inactivated region IR. As a result, it is possible toimprove the drain breakdown voltage.

FIGS. 51 to 56 are each a cross sectional view showing the semiconductordevice of the present embodiment during a manufacturing step. Withreference to FIGS. 55 and 56 which are each a cross sectional viewshowing the final step of FIGS. 51 to 56, a description will be furthergiven to the semiconductor device of Third Embodiment. Incidentally, theplan view of the semiconductor device of the present embodiment is thesame as that of First Embodiment (FIG. 2), except for the trench (T orGLT). For example, FIG. 55 corresponds to the A-A cross section of FIG.2, and FIG. 56 corresponds to a B-B cross section of FIG. 2.Incidentally, the configuration of the present embodiment is the same asthat of First Embodiment, except for the gate electrode part. For thisreason, a detailed description on the same configuration as that ofFirst Embodiment will be omitted.

As shown in FIGS. 55 and 56, in the semiconductor device of the presentembodiment, over a substrate S, there are sequentially formed anucleation layer NUC, a buffer layer BU, a potential fixed layer VC, achannel base layer UC, a channel layer (also referred to as an electrontransit layer) CH, and a barrier layer BA. Then, the semiconductordevice of the present embodiment has a gate electrode GE formed over thebarrier layer BA via a gate junction layer JL, and a source electrode SEand a drain electrode DE formed over the barrier layer BA on theopposite sides of the gate electrode GE, respectively. The semiconductordevice is formed in an active region AC defined by the isolation regionsISO. Under the drain electrode DE, there is arranged a contact hole C1Dserving as a coupling part between the drain electrode DE and thebarrier layer BA. Under the source electrode SE, there is arranged acontact hole C1S serving as a coupling part between the source electrodeSE and the barrier layer BA. Further, the drain electrode DE is coupledwith the drain pad DP, and the source electrode SE is coupled with thesource pad SP. Whereas, the gate electrode GE is coupled with the gateline GL (see FIG. 2).

Herein, the source electrode SE, the drain electrode DE, and the gateelectrode GE are mainly arranged over the active region AC surrounded bythe isolation regions ISO. On the other hand, the drain pad DP, the gateline GL, and the source pad SP are arranged over the isolation regionISO (see FIG. 2).

Then, under the source pad SP, there is arranged a through hole TH. Thethrough hole TH includes a conductive film embedded therein, and formsthe coupling part VIA. As described later, the coupling part VIA iselectrically coupled with the potential fixed layer VC. Accordingly, thesource electrode SE and the potential fixed layer VC are electricallycoupled with each other via the source pad SP and the coupling part VIA.Further, over the source electrode SE and the drain electrode DE, thereis arranged a protective film (also referred to as an insulation film, acovering film, or a surface protective film) PRO.

Further, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Theinactivated region IR reaches the potential fixed layer VC in the depthdirection. Thus, the potential fixed layer VC doped with an impurity toproduce a p type situated between the gate electrode GE and the drainelectrode DE is inactivated by doping of an inactivating element,resulting in the inactivated region IR. As a result, it is possible toimprove the drain breakdown voltage.

The p type potential fixed layer VC situated between the gate electrodeGE and the drain electrode DE contains an inactivating element. Then,the content of the inactivating element in the p type potential fixedlayer VC situated between the gate electrode GE and the drain electrodeDE is larger than the content of the inactivating element in the p typepotential fixed layer VC situated under the source electrode SE. Theinactivating element is, for example, hydrogen (H) or fluorine (F). Theactivation ratio of the inactivated region IR is smaller than, and ispreferably set at 1/10 or less the activation ratio of the region underthe source electrode SE.

Respective constituent materials for the substrate S, the nucleationlayer NUC, the buffer layer BU, the potential fixed layer VC, thechannel base layer UC, the channel layer (also referred to as theelectron transit layer) CH, and the barrier layer BA are as described inFirst Embodiment.

As the gate junction layer JL, there can be used, for example, a GaNlayer. Further, the thickness of the GaN layer can be set at a desirablethickness according to the objective characteristics, and is, forexample, about 50 nm. As the materials for the gate junction layer JL,other than GaN, there can be used AlN, InN, or the like. Incidentally,the gate junction layer JL is preferably doped with a p type impurity.Examples of the p type impurity may include Be, C, and Mg.

Whereas, respective constituent materials for the gate electrode GE, theinterlayer insulation film IL1, and the protective film PRO are asdescribed in First Embodiment.

Further, respective constituent materials for the source electrode SE,the drain electrode DE, the source pad SP, the drain pad DP, and thecoupling part VIA are as described in First Embodiment.

[Manufacturing Method Description]

Then, with reference to FIGS. 51 to 56, a description will be given to amethod for manufacturing the semiconductor device of the presentembodiment. In addition, the configuration of the semiconductor devicewill be made clearer.

As shown in FIG. 51, over a substrate S, there are sequentially formed anucleation layer NUC and a buffer layer BU. For these, the materialsdescribed in First Embodiment are used. Thus, the formation can beachieved in the same manner as in First Embodiment.

Then, over the buffer layer BU, as a potential fixed layer VC, forexample, a gallium nitride layer (p-GaN layer) containing a p typeimpurity is epitaxially grown using the metal organic chemical vapordeposition method, or the like. For example, as a p type impurity, thereis used magnesium (Mg). For example, while doping magnesium (Mg), agallium nitride layer is deposited about 200 nm in thickness. The Mgconcentration in the deposited film is set at, for example, about 5×10¹⁸(5E18) cm⁻³.

Then, over the potential fixed layer VC, there are sequentially formed achannel base layer UC, a channel layer CH, and a barrier layer BA. Forthese, the materials described in First Embodiment are used. Thus, theformation can be achieved in the same manner as in First Embodiment.Then, in the same manner as in First Embodiment, there is formed anisolation region ISO.

Then, over the barrier layer BA, as a gate junction layer JL, forexample, a gallium nitride layer (p-GaN layer) containing a p typeimpurity is epitaxially grown using the metal organic chemical vapordeposition method, or the like. For example, as a p type impurity, thereis used magnesium (Mg). For example, while doping magnesium (Mg), agallium nitride layer is deposited about 50 nm in thickness.

Then, over the gate junction layer JL, there is formed a photoresistfilm having an opening in the gate electrode formation region. Using thephotoresist film as a mask, the gate junction layer JL is dry etched.

Then, as shown in FIG. 52, an inactivating element is ion implanted,thereby to form an inactivated region IR. For example, using aphotolithography technology, there is formed a photoresist film PR50having an opening in the formation region of the inactivated region IR.Using the photoresist film PR50 as a mask, an inactivating element isimplanted into the potential fixed layer VC on one side of the gateelectrode GE (on the right side in FIG. 52, or the drain electrodeside). As a result, there is formed the inactivated region IR.Incidentally, herein, in consideration of diffusion of the inactivatingelement, there is shown the state in which an inactivating element isimplanted into the lamination part of the potential fixed layer VC, thechannel base layer UC, the channel layer CH, and the barrier layer BAsituated on one side of the gate electrode GE.

Then, as shown in FIGS. 53 and 54, over the gate junction layer JL,there is formed a gate electrode GE. For example, over the gate junctionlayer JL, as a conductive film, for example, a TiN (titanium nitride)film is deposited with a film thickness of about 200 nm using asputtering method, or the like. Then, the TiN film is etched, thereby toform the gate electrode GE.

Then, over the barrier layer BA including over the gate electrode GE, aninterlayer insulation film IL1 is formed in the same manner as in FirstEmbodiment.

Then, contact holes C1S and C1D, and a through hole TH are formed in theinterlayer insulation film IL1 in the same manner as with FirstEmbodiment.

From the bottom surfaces of the contact holes C1S and C1D formed in thestep described above, the barrier layer BA is exposed. From the bottomsurface of the through hole TH, the potential fixed layer VC is exposed.

Then, as shown in FIGS. 55 and 56, over the interlayer insulation filmIL1 including the insides of the contact holes C1S and C1D, and thethrough hole TH, there is formed a conductive film, thereby to form asource electrode SE, a drain electrode DE, a source pad SP, a drain pad(DP), and a coupling part VIA. For these, the materials described inFirst Embodiment are used, and the formation can be achieved in the samemanner as in First Embodiment.

Then, a protective film PRO is formed over the interlayer insulationfilm IL1 including over the source electrode SE, the drain electrode DE,the source pad SP, and the drain pad (DP) in the same manner as in FirstEmbodiment.

By the steps up to this point, it is possible to form the semiconductordevice of the present embodiment. Incidentally, the steps describedabove are examples. The semiconductor device of the present embodimentmay also be manufactured by other steps than the steps described above.

Fourth Embodiment

In First Embodiment, the recess gate type semiconductor device was shownas an example. However, semiconductor devices with other configurationsare also acceptable. For example, as in the present embodiment, theremay be used a semiconductor device not having a gate insulation filmunder the gate electrode.

Below, with reference to the accompanying drawings, a semiconductordevice of the present embodiment will be described in details.

[Structure Description]

FIG. 57 is a cross sectional view schematically showing a configurationof the semiconductor device of the present embodiment. The semiconductordevice (semiconductor element) of the present embodiment is a transistorusing a nitride semiconductor. The semiconductor device can be used as ahigh electron mobility transistor (HEMT) type power transistor.

In the semiconductor device of the present embodiment, as with FirstEmbodiment, over a substrate S, there are sequentially formed anucleation layer NUC, a buffer layer BU, a potential fixed layer VC, achannel base layer UC, a channel layer (also referred to as an electrontransit layer) CH, and a barrier layer BA. The nucleation layer NUC isformed of a nitride semiconductor layer. The buffer layer BU is formedof a single layered or multilayered nitride semiconductor layer dopedwith an impurity for forming a deep level in a nitride semiconductor.Herein, there is used a superlattice structure formed of a multilayernitride semiconductor layer. The potential fixed layer VC is formed of anitride semiconductor layer doped with an impurity to produce a p typewith respect to a nitride semiconductor, and has a conductivity. Thechannel base layer UC is formed of a nitride semiconductor layer smallerin electron affinity than the channel layer CH, and smaller in averagelattice constant in the substrate surface direction than the channellayer CH. The channel layer CH is formed of a nitride semiconductorlayer larger in electron affinity than the channel base layer UC. Thebarrier layer BA is formed of a nitride semiconductor layer smaller inelectron affinity than the channel layer CH, and smaller in electronaffinity than the channel base layer UC.

The semiconductor device of the present embodiment has the gateelectrode GE formed over the barrier layer BA, and the source electrodeSE and the drain electrode DE formed over the barrier layer BA on theopposite sides of the gate electrode GE, respectively. The semiconductordevice is formed in the active region AC defined by the isolationregions ISO.

On the channel layer CH side in the vicinity of the interface betweenthe channel layer CH and the barrier layer BA, there is generated atwo-dimensional electron gas (2DEG). By applying the gate electrode GEwith a prescribed potential, it is possible to eliminate thetwo-dimensional electron gas (2DEG), resulting in the OFF state.

Herein, in the present embodiment, in the isolation region ISO, there isprovided a coupling part (also referred to as a via) VIA penetratingthrough the isolation region ISO, and reaching the underlying potentialfixed layer VC. The coupling part VIA is electrically coupled with thesource electrode SE. Thus, the potential fixed layer VC is provided, andcoupled with the source electrode SE. As a result, it is possible toreduce the fluctuations in characteristics such as the thresholdpotential and the ON resistance.

Further, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Theinactivated region IR reaches the potential fixed layer VC in the depthdirection. Thus, the potential fixed layer VC doped with an impurity toproduce a p type situated between the gate electrode GE and the drainelectrode DE is inactivated by doping of an inactivating element,resulting in the inactivated region IR. As a result, it is possible toimprove the drain breakdown voltage.

FIGS. 58 to 60 are each a cross sectional view showing the semiconductordevice of the present embodiment during a manufacturing step. Withreference to FIG. 60 which is a cross sectional view showing the finalstep of FIGS. 58 to 60, a description will be further given to thesemiconductor device of Fourth Embodiment. Incidentally, the plan viewof the semiconductor device of the present embodiment is the same asthat of First Embodiment (FIG. 2), except for the trench (T or GLT). Forexample, FIG. 60 corresponds to the A-A cross section of FIG. 2.Further, the configuration of the present embodiment is the same as thatof First Embodiment, except for the gate electrode part. For thisreason, a detailed description on the same configuration as that ofFirst Embodiment will be omitted.

As shown in FIG. 60, in the semiconductor device of the presentembodiment, over a substrate S, there are sequentially formed anucleation layer NUC, a buffer layer BU, a potential fixed layer VC, achannel base layer UC, a channel layer (also referred to as an electrontransit layer) CH, and a barrier layer BA. Then, the semiconductordevice of the present embodiment has a gate electrode GE formed over thebarrier layer BA, and a source electrode SE and a drain electrode DEformed over the barrier layer BA on the opposite sides of the gateelectrode GE, respectively. The semiconductor device is formed in anactive region AC defined by the element isolation regions (ISO). Underthe drain electrode DE, there is arranged a contact hole C1D serving asa coupling part between the drain electrode DE and the barrier layer BA.Under the source electrode SE, there is arranged a contact hole C1Sserving as a coupling part between the source electrode SE and thebarrier layer BA. Further, the drain electrode DE is coupled with thedrain pad DP, and the source electrode SE is coupled with the source padSP. Whereas, the gate electrode GE is coupled with the gate line GL (seeFIG. 2).

Herein, the source electrode SE, the drain electrode DE, and the gateelectrode GE are mainly arranged over the active region AC surrounded bythe isolation regions ISO. On the other hand, the drain pad DP, the gateline GL, and the source pad SP are arranged over the isolation regionISO (see FIG. 2). Further, also in the present embodiment, as with FirstEmbodiment, under the source pad SP, there is arranged a coupling partVIA (through hole TH).

Further, over the gate electrode GE, there is arranged an interlayerinsulation film IL1. Over the source electrode SE and the drainelectrode DE, there is arranged a protective film (also referred to asan insulation film, a covering film, or a surface protective film) PRO.

Further, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Theinactivated region IR reaches the potential fixed layer VC in the depthdirection. Thus, the potential fixed layer VC doped with an impurity toproduce a p type situated between the gate electrode GE and the drainelectrode DE is inactivated by doping of an inactivating element,resulting in the inactivated region IR. As a result, it is possible toimprove the drain breakdown voltage.

The p type potential fixed layer VC situated between the gate electrodeGE and the drain electrode DE contains an inactivating element. Then,the content of the inactivating element in the p type potential fixedlayer VC situated between the gate electrode GE and the drain electrodeDE is larger than the content of the inactivating element in the p typepotential fixed layer VC situated under the source electrode SE. Theinactivating element is, for example, hydrogen (H) or fluorine (F). Theactivation ratio of the inactivated region IR is smaller than, and ispreferably set at 1/10 or less the activation ratio of the region underthe source electrode SE.

Respective constituent materials for the substrate S, the nucleationlayer NUC, the buffer layer BU, the potential fixed layer VC, thechannel base layer UC, the channel layer (also referred to as anelectron transit layer) CH, and the barrier layer BA are as described inFirst Embodiment.

Whereas, respective constituent materials for the gate electrode GE, theinterlayer insulation film IL1, and the protective film PRO are asdescribed in First Embodiment.

Whereas, respective constituent materials for the source electrode SE,the drain electrode DE, the source pad SP, the drain pad DP, and thecoupling part VIA are as described in First Embodiment.

[Manufacturing Method Description]

Then, with reference to FIGS. 58 to 60, a description will be given to amethod for manufacturing the semiconductor device of the presentembodiment. In addition, the configuration of the semiconductor devicewill be made clearer.

As shown in FIG. 58, over a substrate S, there are sequentially formed anucleation layer NUC and a buffer layer BU. For these, the materialsdescribed in First Embodiment are used. Thus, the formation can beachieved in the same manner as in First Embodiment.

Then, over the buffer layer BU, as a potential fixed layer VC, forexample, a gallium nitride layer (p-GaN layer) containing a p typeimpurity is epitaxially grown using the metal organic chemical vapordeposition method, or the like. For example, as a p type impurity, thereis used magnesium (Mg). For example, while doping magnesium (Mg), agallium nitride layer is deposited about 200 nm in thickness. The Mgconcentration in the deposited film is set at, for example, about 5×10¹⁸(5E18) cm⁻³.

Then, over the potential fixed layer VC, there are sequentially formed achannel base layer UC, a channel layer CH, and a barrier layer BA. Forthese, the materials described in First Embodiment are used. Thus, theformation can be achieved in the same manner as in First Embodiment.

Then, over the barrier layer BA, as an insulation film IF60, a siliconnitride film is deposited using a sputtering method, or the like. Then,the insulation film IF60 is provided therein with an opening. Over theinsulation film IF60 including the inside of the opening, there isformed a gate electrode GE. The gate electrode GE can be formed in thesame manner as in First Embodiment.

Then, as shown in FIG. 59, an inactivating element is ion implanted,thereby to form an inactivated region IR. For example, using aphotolithography technology, there is formed a photoresist film PR60having an opening in the formation region of the inactivated region IR.Using the photoresist film PR60 as a mask, an inactivating element isimplanted into the potential fixed layer VC on one side of the gateelectrode GE (on the right side in FIG. 59, or the drain electrodeside). As a result, there is formed the inactivated region IR.Incidentally, herein, in consideration of diffusion of the inactivatingelement, there is shown the state in which an inactivating element isimplanted into the lamination part of the potential fixed layer VC, thechannel base layer UC, the channel layer CH, and the barrier layer BAsituated on one side of the gate electrode GE.

Then, as shown in FIG. 60, over the barrier layer BA including over thegate electrode GE, an interlayer insulation film IL1 is formed in thesame manner as in First Embodiment.

Then, contact holes C1S and C1D, and the like are formed in theinterlayer insulation film IL1 in the same manner as in FirstEmbodiment. Then, over the interlayer insulation film IL1 including theinsides of the contact holes C1S and C1D, there is formed a conductivefilm. As a result, there are formed a source electrode SE, a drainelectrode DE, and the like (see FIG. 2). For these, the materialsdescribed in First Embodiment are used. Thus, the formation can beachieved in the same manner as in First Embodiment.

Then, a protective film PRO is formed over the interlayer insulationfilm IL1 including the source electrode SE, the drain electrode DE, andthe like in the same manner as in First Embodiment.

By the steps up to this point, it is possible to form the semiconductordevice of the present embodiment. Incidentally, the steps describedabove are examples. The semiconductor device of the present embodimentmay also be manufactured by other steps than the steps described above.

Fifth Embodiment

In First Embodiment, in the isolation region ISO, there was provided thecoupling part VIA. However, in the active region AC, there may beprovided the coupling part VIA. For example, in the present embodiment,under the source electrode SE, there is provided the coupling part VIA.

Below, with reference to the accompanying drawings, a semiconductordevice of the present embodiment will be described in details.Incidentally, the same configuration as that of First Embodiment willnot be described.

FIG. 61 is a cross sectional view schematically showing a configurationof the semiconductor device of the present embodiment. FIG. 62 is across sectional view showing a configuration of the semiconductor deviceof the present embodiment. FIG. 63 is a plan view showing aconfiguration of the semiconductor device of the present embodiment. Thesemiconductor device (semiconductor element) of the present embodimentis a MIS type field effect transistor using a nitride semiconductor. Thesemiconductor device can be used as a high electron mobility transistor(HEMT) type power transistor. The semiconductor device of the presentembodiment is a so-called recess gate type semiconductor device.

In the semiconductor device of the present embodiment, as shown in FIGS.61 to 63, under the source electrode SE in the active region AC, thereis provided a coupling part (also referred as a via) VIA penetratingthrough the barrier layer BA, the channel layer CH, and the channel baselayer UC, and the underlying potential fixed layer VC. The coupling partVIA is electrically coupled with the source electrode SE. Thus, thepotential fixed layer VC is provided, and is coupled with the sourceelectrode SE. As a result, as described in First Embodiment, it ispossible to reduce the fluctuations in characteristics such as thethreshold potential and the ON resistance. Further, the coupling partVIA is arranged in the active region AC in which electrons areconducted. For this reason, it is possible to fix the potential moreeffectively (see FIG. 63).

Further, in the present embodiment, an inactivated region IR is providedbetween the gate electrode GE and the drain electrode DE. Theinactivated region IR reaches the potential fixed layer VC in the depthdirection. Thus, the potential fixed layer VC doped with an impurity toproduce a p type situated between the gate electrode GE and the drainelectrode DE is inactivated by doping of an inactivating element,resulting in the inactivated region IR. As a result, it is possible toimprove the drain breakdown voltage.

FIGS. 64A and 64B are cross sectional views schematically showing otherconfigurations of the semiconductor device of the present embodiment. Asshown in FIG. 64A, the following configuration is also acceptable: thebottom surface of the through hole TH is arranged at the top surface ofthe potential fixed layer VC; and the bottom of the coupling part VIAand the potential fixed layer VC are in contact with each other.Whereas, as shown in FIG. 64B, the following configuration is alsoacceptable: the bottom surface of the through hole TH in which thecoupling part VIA is arranged, is arranged below the bottom surface ofthe potential fixed layer VC; and a part of the side surface of thecoupling part VIA is in contact with the potential fixed layer VC. Thus,it is essential only that the coupling part VIA is arranged in such amanner as to be in contact with the potential fixed layer VC.

The semiconductor device of the present embodiment (FIGS. 61 and 64) canbe formed by the same steps as those in First Embodiment, except foronly changing the position or depth of the through hole TH.

FIG. 65 is a cross sectional view schematically showing anotherconfiguration of the semiconductor device of the present embodiment. Thesemiconductor device shown in FIG. 65 is obtained by omitting theconfiguration of the channel base layer UC and the coupling part VIAfrom the semiconductor device shown in FIG. 57. Thus, the channel baselayer UC and the coupling part VIA may be omitted (the same also appliesto First Embodiment and the like). Whereas, in First Embodiment, or thelike, as the potential fixed layer VC, a GaN layer was used, but anAlGaN layer may also be used. When an AlGaN layer is used as the channelbase layer UC, the potential fixed layer VC and the channel base layerUC are formed of the same material. However, the potential fixed layerVC is doped with an impurity.

Up to this point, the invention completed by the present inventors wasspecifically described by way of embodiments. However, it is naturallyunderstood that the present invention is not limited to the embodiments,and may be variously changed within the scope not departing from thegist thereof. For example, the configuration obtained by omitting thecoupling part VIA described in Applied Example 3 of First Embodiment maybe applied to the semiconductor devices of Second to Fourth Embodiments.Whereas, the coupling part VIA of First or Second Embodiment may bearranged under the source electrode SE in the active region AC asdescribed in Fifth Embodiment. Further, the position of the bottomsurface of the coupling part VIA of First or Second Embodiment may bechanged as described in Fifth Embodiment. Alternatively, other thanthese, various combinations are possible in the configuration or themanufacturing step of each site described in each embodiment.

What is claimed is:
 1. A semiconductor device, comprising: a firstnitride semiconductor layer formed over a substrate, and containing a ptype impurity; a gate electrode formed over the first nitridesemiconductor layer; and a first electrode and a second electrode formedon the opposite sides of the gate electrode, respectively, wherein thefirst nitride semiconductor layer has an inactivated region between thegate electrode and the second electrode, and wherein the inactivatedregion is a region containing an inactivating element.
 2. Thesemiconductor device according to claim 1, wherein the inactivatingelement is hydrogen or fluorine.
 3. The semiconductor device accordingto claim 1, wherein the first nitride semiconductor layer is of a ptype, and contains magnesium as a p type impurity.
 4. The semiconductordevice according to claim 3, wherein the inactivating element ishydrogen.
 5. The semiconductor device according to claim 1, having acoupling part for establishing a coupling between the first electrodeand the first nitride semiconductor layer.
 6. The semiconductor deviceaccording to claim 5, including: a second nitride semiconductor layerformed over the first nitride semiconductor layer; a third nitridesemiconductor layer formed over the second nitride semiconductor layer;and a trench penetrating through the third nitride semiconductor layer,and reaching some point of the second nitride semiconductor layer,wherein the gate electrode is arranged in the trench via a gateinsulation film, and wherein the electron affinity of the second nitridesemiconductor layer is larger than the electron affinity of the thirdnitride semiconductor layer.
 7. The semiconductor device according toclaim 6, wherein the substrate has a first region and a second region,wherein the gate electrode, the first electrode, and the secondelectrode are formed in the first region, wherein the second region isan element isolation region formed in the third nitride semiconductorlayer and the second nitride semiconductor layer, and wherein thecoupling part is arranged in the inside of a through hole penetratingthrough the element isolation region and the second nitridesemiconductor layer, and reaching the first nitride semiconductor layer.8. The semiconductor device according to claim 6, having a superlatticelayer between the substrate and the first nitride semiconductor layer,wherein the superlattice layer includes two or more laminates each of afifth nitride semiconductor layer, and a sixth nitride semiconductorlayer different in electron affinity from the fifth nitridesemiconductor layer repeatedly arranged therein.
 9. A semiconductordevice, comprising: a first nitride semiconductor layer formed over asubstrate, and containing a p type impurity; a second nitridesemiconductor layer formed over the first nitride semiconductor layer; athird nitride semiconductor layer formed over the second nitridesemiconductor layer; a fourth nitride semiconductor layer formed overthe third nitride semiconductor layer; a trench penetrating through thefourth nitride semiconductor layer, and reaching some point of the thirdnitride semiconductor layer; a gate electrode arranged in the trench viaa gate insulation film; and a first electrode and a second electrodeformed over the fourth nitride semiconductor layer on the opposite sidesof the gate electrode, respectively, wherein the electron affinity ofthe third nitride semiconductor layer is larger than the electronaffinity of the second nitride semiconductor layer, wherein the electronaffinity of the fourth nitride semiconductor layer is smaller than theelectron affinity of the second nitride semiconductor layer, wherein thefirst nitride semiconductor layer has an inactivated region between thegate electrode and the second electrode, wherein the inactivated regionis a region containing an inactivating element, and wherein the gateinsulation film extends from under the gate electrode to the firstelectrode.
 10. The semiconductor device according to claim 9, whereinthe inactivating element is hydrogen or fluorine.
 11. The semiconductordevice according to claim 9, wherein the first nitride semiconductorlayer is of a p type, and contains magnesium as a p type impurity. 12.The semiconductor device according to claim 11, wherein the inactivatingelement is hydrogen.
 13. The semiconductor device according to claim 9,having a coupling part for establishing a coupling between the firstelectrode and the first nitride semiconductor layer.
 14. Thesemiconductor device according to claim 13, wherein the substrate has afirst region and a second region, wherein the gate electrode, the firstelectrode, and the second electrode are formed in the first region,wherein the second region is an element isolation region formed in thefourth nitride semiconductor layer and the third nitride semiconductorlayer, and wherein the coupling part is arranged in the inside of athrough hole penetrating through the gate insulation film, the elementisolation region, and the second nitride semiconductor layer, andreacting the first nitride semiconductor layer.
 15. The semiconductordevice according to claim 13, having a superlattice layer between thesubstrate and the first nitride semiconductor layer, wherein thesuperlattice layer includes two or more laminates each of a fifthnitride semiconductor layer, and a sixth nitride semiconductor layerdifferent in electron affinity from the fifth nitride semiconductorlayer repeatedly arranged therein.
 16. A method for manufacturing asemiconductor device, comprising the steps of: (a) forming a firstnitride semiconductor layer containing a p type impurity over asubstrate, (b) forming a second nitride semiconductor layer over thefirst nitride semiconductor layer, (c) forming a third nitridesemiconductor layer over the second nitride semiconductor layer, (d)forming a fourth nitride semiconductor layer over the third nitridesemiconductor layer, (e) forming a trench penetrating through the fourthnitride semiconductor layer, and reaching some point of the thirdnitride semiconductor layer, (f) forming a gate electrode in the trenchvia a gate insulation film, (g) introducing an inactivating element intothe first nitride semiconductor layer situated on one side of the gateelectrode, and (h) forming a first electrode over the fourth nitridesemiconductor layer on the other side of the gate electrode, and forminga second electrode over the fourth nitride semiconductor layer on theone side of the gate electrode, wherein the electron affinity of thethird nitride semiconductor layer is larger than the electron affinityof the second nitride semiconductor layer, and wherein the electronaffinity of the fourth nitride semiconductor layer is smaller than theelectron affinity of the second nitride semiconductor layer.
 17. Themethod for manufacturing a semiconductor device according to claim 16,wherein the inactivating element is hydrogen or fluorine.
 18. The methodfor manufacturing a semiconductor device according to claim 16, whereinthe first nitride semiconductor layer is of a p type, and containsmagnesium as a p type impurity.
 19. The method for manufacturing asemiconductor device according to claim 18, wherein the inactivatingelement is hydrogen.
 20. The method for manufacturing a semiconductordevice according to claim 16, the method having a step of forming acoupling part for establishing a coupling between the first electrodeand the first nitride semiconductor layer.
 21. The method formanufacturing a semiconductor device according to claim 16, wherein thestep (g) is a step of introducing the inactivating element into thefirst nitride semiconductor layer with the gate insulation film leftover the first nitride semiconductor layer situated on the other side ofthe gate electrode.